diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index e8cff8b..8cf9172 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -114,53 +114,14 @@ function drupal_theme_rebuild() {
  *
  * @return array
  *   The functions found, suitable for returning from hook_theme;
+ *
+ * @deprecated in Drupal 8.x-dev and will be removed before Drupal 9.0.0. Use
+ *   the theme.registry service.
+ *
+ * @see Drupal\Core\Theme\Registry::findThemeFunctions()
  */
 function drupal_find_theme_functions($cache, $prefixes) {
-  $implementations = [];
-  $grouped_functions = \Drupal::service('theme.registry')->getPrefixGroupedUserFunctions();
-
-  foreach ($cache as $hook => $info) {
-    foreach ($prefixes as $prefix) {
-      // Find theme functions that implement possible "suggestion" variants of
-      // registered theme hooks and add those as new registered theme hooks.
-      // The 'pattern' key defines a common prefix that all suggestions must
-      // start with. The default is the name of the hook followed by '__'. An
-      // 'base hook' key is added to each entry made for a found suggestion,
-      // so that common functionality can be implemented for all suggestions of
-      // the same base hook. To keep things simple, deep hierarchy of
-      // suggestions is not supported: each suggestion's 'base hook' key
-      // refers to a base hook, not to another suggestion, and all suggestions
-      // are found using the base hook's pattern, not a pattern from an
-      // intermediary suggestion.
-      $pattern = isset($info['pattern']) ? $info['pattern'] : ($hook . '__');
-      // Grep only the functions which are within the prefix group.
-      list($first_prefix,) = explode('_', $prefix, 2);
-      if (!isset($info['base hook']) && !empty($pattern) && isset($grouped_functions[$first_prefix])) {
-        $matches = preg_grep('/^' . $prefix . '_' . $pattern . '/', $grouped_functions[$first_prefix]);
-        if ($matches) {
-          foreach ($matches as $match) {
-            $new_hook = substr($match, strlen($prefix) + 1);
-            $arg_name = isset($info['variables']) ? 'variables' : 'render element';
-            $implementations[$new_hook] = array(
-              'function' => $match,
-              $arg_name => $info[$arg_name],
-              'base hook' => $hook,
-            );
-          }
-        }
-      }
-      // Find theme functions that implement registered theme hooks and include
-      // that in what is returned so that the registry knows that the theme has
-      // this implementation.
-      if (function_exists($prefix . '_' . $hook)) {
-        $implementations[$hook] = array(
-          'function' => $prefix . '_' . $hook,
-        );
-      }
-    }
-  }
-
-  return $implementations;
+  return \Drupal::service('theme.registry')->findThemeFunctions($cache, $prefixes);
 }
 
 /**
@@ -172,100 +133,14 @@ function drupal_find_theme_functions($cache, $prefixes) {
  *   The extension that these templates will have.
  * @param $path
  *   The path to search.
+ *
+ * @deprecated in Drupal 8.x-dev and will be removed before Drupal 9.0.0. Use
+ *   the theme.registry service.
+ *
+ * @see Drupal\Core\Theme\Registry::findThemeTemplates()
  */
 function drupal_find_theme_templates($cache, $extension, $path) {
-  $implementations = array();
-
-  // Collect paths to all sub-themes grouped by base themes. These will be
-  // used for filtering. This allows base themes to have sub-themes in its
-  // folder hierarchy without affecting the base themes template discovery.
-  $theme_paths = array();
-  foreach (\Drupal::service('theme_handler')->listInfo() as $theme_info) {
-    if (!empty($theme_info->base_theme)) {
-      $theme_paths[$theme_info->base_theme][$theme_info->getName()] = $theme_info->getPath();
-    }
-  }
-  foreach ($theme_paths as $basetheme => $subthemes) {
-    foreach ($subthemes as $subtheme => $subtheme_path) {
-      if (isset($theme_paths[$subtheme])) {
-        $theme_paths[$basetheme] = array_merge($theme_paths[$basetheme], $theme_paths[$subtheme]);
-      }
-    }
-  }
-  $theme = \Drupal::theme()->getActiveTheme()->getName();
-  $subtheme_paths = isset($theme_paths[$theme]) ? $theme_paths[$theme] : array();
-
-  // Escape the periods in the extension.
-  $regex = '/' . str_replace('.', '\.', $extension) . '$/';
-  // Get a listing of all template files in the path to search.
-  $files = file_scan_directory($path, $regex, array('key' => 'filename'));
-
-  // Find templates that implement registered theme hooks and include that in
-  // what is returned so that the registry knows that the theme has this
-  // implementation.
-  foreach ($files as $template => $file) {
-    // Ignore sub-theme templates for the current theme.
-    if (strpos($file->uri, str_replace($subtheme_paths, '', $file->uri)) !== 0) {
-      continue;
-    }
-    // Remove the extension from the filename.
-    $template = str_replace($extension, '', $template);
-    // Transform - in filenames to _ to match function naming scheme
-    // for the purposes of searching.
-    $hook = strtr($template, '-', '_');
-    if (isset($cache[$hook])) {
-      $implementations[$hook] = array(
-        'template' => $template,
-        'path' => dirname($file->uri),
-      );
-    }
-
-    // Match templates based on the 'template' filename.
-    foreach ($cache as $hook => $info) {
-      if (isset($info['template'])) {
-        $template_candidates = array($info['template'], str_replace($info['theme path'] . '/templates/', '', $info['template']));
-        if (in_array($template, $template_candidates)) {
-          $implementations[$hook] = array(
-            'template' => $template,
-            'path' => dirname($file->uri),
-          );
-        }
-      }
-    }
-  }
-
-  // Find templates that implement possible "suggestion" variants of registered
-  // theme hooks and add those as new registered theme hooks. See
-  // drupal_find_theme_functions() for more information about suggestions and
-  // the use of 'pattern' and 'base hook'.
-  $patterns = array_keys($files);
-  foreach ($cache as $hook => $info) {
-    $pattern = isset($info['pattern']) ? $info['pattern'] : ($hook . '__');
-    if (!isset($info['base hook']) && !empty($pattern)) {
-      // Transform _ in pattern to - to match file naming scheme
-      // for the purposes of searching.
-      $pattern = strtr($pattern, '_', '-');
-
-      $matches = preg_grep('/^' . $pattern . '/', $patterns);
-      if ($matches) {
-        foreach ($matches as $match) {
-          $file = $match;
-          // Remove the extension from the filename.
-          $file = str_replace($extension, '', $file);
-          // Put the underscores back in for the hook name and register this
-          // pattern.
-          $arg_name = isset($info['variables']) ? 'variables' : 'render element';
-          $implementations[strtr($file, '-', '_')] = array(
-            'template' => $file,
-            'path' => dirname($files[$match]->uri),
-            $arg_name => $info[$arg_name],
-            'base hook' => $hook,
-          );
-        }
-      }
-    }
-  }
-  return $implementations;
+  return \Drupal::service('theme.registry')->findThemeTemplates($cache, $extension, $path);
 }
 
 /**
diff --git a/core/lib/Drupal/Core/Theme/Registry.php b/core/lib/Drupal/Core/Theme/Registry.php
index 0167a74..677250d 100644
--- a/core/lib/Drupal/Core/Theme/Registry.php
+++ b/core/lib/Drupal/Core/Theme/Registry.php
@@ -766,4 +766,168 @@ public function getPrefixGroupedUserFunctions() {
   protected function getPath($module) {
     return drupal_get_path('module', $module);
   }
+
+  /**
+   * Allows themes and/or theme engines to easily discover overridden templates.
+   *
+   * @param $cache
+   *   The existing cache of theme hooks to test against.
+   * @param $extension
+   *   The extension that these templates will have.
+   * @param $path
+   *   The path to search.
+   */
+  public function findThemeTemplates($cache, $extension, $path) {
+    $implementations = array();
+
+    // Collect paths to all sub-themes grouped by base themes. These will be
+    // used for filtering. This allows base themes to have sub-themes in its
+    // folder hierarchy without affecting the base themes template discovery.
+    $theme_paths = array();
+    foreach ($this->themeHandler->listInfo() as $theme_info) {
+      if (!empty($theme_info->base_theme)) {
+        $theme_paths[$theme_info->base_theme][$theme_info->getName()] = $theme_info->getPath();
+      }
+    }
+    foreach ($theme_paths as $basetheme => $subthemes) {
+      foreach ($subthemes as $subtheme => $subtheme_path) {
+        if (isset($theme_paths[$subtheme])) {
+          $theme_paths[$basetheme] = array_merge($theme_paths[$basetheme], $theme_paths[$subtheme]);
+        }
+      }
+    }
+    $theme = $this->themeManager->getActiveTheme()->getName();
+    $subtheme_paths = isset($theme_paths[$theme]) ? $theme_paths[$theme] : array();
+
+    // Escape the periods in the extension.
+    $regex = '/' . str_replace('.', '\.', $extension) . '$/';
+    // Get a listing of all template files in the path to search.
+    $files = file_scan_directory($path, $regex, array('key' => 'filename'));
+
+    // Find templates that implement registered theme hooks and include that in
+    // what is returned so that the registry knows that the theme has this
+    // implementation.
+    foreach ($files as $template => $file) {
+      // Ignore sub-theme templates for the current theme.
+      if (strpos($file->uri, str_replace($subtheme_paths, '', $file->uri)) !== 0) {
+        continue;
+      }
+      // Remove the extension from the filename.
+      $template = str_replace($extension, '', $template);
+      // Transform - in filenames to _ to match function naming scheme
+      // for the purposes of searching.
+      $hook = strtr($template, '-', '_');
+      if (isset($cache[$hook])) {
+        $implementations[$hook] = array(
+          'template' => $template,
+          'path' => dirname($file->uri),
+        );
+      }
+
+      // Match templates based on the 'template' filename.
+      foreach ($cache as $hook => $info) {
+        if (isset($info['template'])) {
+          $template_candidates = array($info['template'], str_replace($info['theme path'] . '/templates/', '', $info['template']));
+          if (in_array($template, $template_candidates)) {
+            $implementations[$hook] = array(
+              'template' => $template,
+              'path' => dirname($file->uri),
+            );
+          }
+        }
+      }
+    }
+
+    // Find templates that implement possible "suggestion" variants of registered
+    // theme hooks and add those as new registered theme hooks. See
+    // drupal_find_theme_functions() for more information about suggestions and
+    // the use of 'pattern' and 'base hook'.
+    $patterns = array_keys($files);
+    foreach ($cache as $hook => $info) {
+      $pattern = isset($info['pattern']) ? $info['pattern'] : ($hook . '__');
+      if (!isset($info['base hook']) && !empty($pattern)) {
+        // Transform _ in pattern to - to match file naming scheme
+        // for the purposes of searching.
+        $pattern = strtr($pattern, '_', '-');
+
+        $matches = preg_grep('/^' . $pattern . '/', $patterns);
+        if ($matches) {
+          foreach ($matches as $match) {
+            $file = $match;
+            // Remove the extension from the filename.
+            $file = str_replace($extension, '', $file);
+            // Put the underscores back in for the hook name and register this
+            // pattern.
+            $arg_name = isset($info['variables']) ? 'variables' : 'render element';
+            $implementations[strtr($file, '-', '_')] = array(
+              'template' => $file,
+              'path' => dirname($files[$match]->uri),
+              $arg_name => $info[$arg_name],
+              'base hook' => $hook,
+            );
+          }
+        }
+      }
+    }
+    return $implementations;
+  }
+
+  /**
+   * Allows themes and/or theme engines to discover overridden theme functions.
+   *
+   * @param array $cache
+   *   The existing cache of theme hooks to test against.
+   * @param array $prefixes
+   *   An array of prefixes to test, in reverse order of importance.
+   *
+   * @return array
+   *   The functions found, suitable for returning from hook_theme;
+   */
+  public function findThemeFunctions($cache, $prefixes) {
+    $implementations = [];
+    $grouped_functions = $this->getPrefixGroupedUserFunctions();
+
+    foreach ($cache as $hook => $info) {
+      foreach ($prefixes as $prefix) {
+        // Find theme functions that implement possible "suggestion" variants of
+        // registered theme hooks and add those as new registered theme hooks.
+        // The 'pattern' key defines a common prefix that all suggestions must
+        // start with. The default is the name of the hook followed by '__'. An
+        // 'base hook' key is added to each entry made for a found suggestion,
+        // so that common functionality can be implemented for all suggestions of
+        // the same base hook. To keep things simple, deep hierarchy of
+        // suggestions is not supported: each suggestion's 'base hook' key
+        // refers to a base hook, not to another suggestion, and all suggestions
+        // are found using the base hook's pattern, not a pattern from an
+        // intermediary suggestion.
+        $pattern = isset($info['pattern']) ? $info['pattern'] : ($hook . '__');
+        // Grep only the functions which are within the prefix group.
+        list($first_prefix,) = explode('_', $prefix, 2);
+        if (!isset($info['base hook']) && !empty($pattern) && isset($grouped_functions[$first_prefix])) {
+          $matches = preg_grep('/^' . $prefix . '_' . $pattern . '/', $grouped_functions[$first_prefix]);
+          if ($matches) {
+            foreach ($matches as $match) {
+              $new_hook = substr($match, strlen($prefix) + 1);
+              $arg_name = isset($info['variables']) ? 'variables' : 'render element';
+              $implementations[$new_hook] = array(
+                'function' => $match,
+                $arg_name => $info[$arg_name],
+                'base hook' => $hook,
+              );
+            }
+          }
+        }
+        // Find theme functions that implement registered theme hooks and include
+        // that in what is returned so that the registry knows that the theme has
+        // this implementation.
+        if (function_exists($prefix . '_' . $hook)) {
+          $implementations[$hook] = array(
+            'function' => $prefix . '_' . $hook,
+          );
+        }
+      }
+    }
+
+    return $implementations;
+  }
 }