diff -u b/core/modules/block/src/Tests/BlockTest.php b/core/modules/block/src/Tests/BlockTest.php
--- b/core/modules/block/src/Tests/BlockTest.php
+++ b/core/modules/block/src/Tests/BlockTest.php
@@ -338,7 +338,7 @@
       'rendered',
     );
     sort($expected_cache_tags);
-    $keys = \Drupal::service('cache_contexts_manager')->convertTokensToKeys(['languages:language_interface', 'theme', 'user.permissions']);
+    $keys = \Drupal::service('cache_contexts_manager')->convertTokensToKeys(['languages:language_interface', 'theme', 'user.permissions'])->getKeys();
     $this->assertIdentical($cache_entry->tags, $expected_cache_tags);
     $cache_entry = \Drupal::cache('render')->get('entity_view:block:powered:' . implode(':', $keys));
     $expected_cache_tags = array(
@@ -386,7 +386,7 @@
       'rendered',
     );
     sort($expected_cache_tags);
-    $keys = \Drupal::service('cache_contexts_manager')->convertTokensToKeys(['languages:language_interface', 'theme', 'user.permissions']);
+    $keys = \Drupal::service('cache_contexts_manager')->convertTokensToKeys(['languages:language_interface', 'theme', 'user.permissions'])->getKeys();
     $cache_entry = \Drupal::cache('render')->get('entity_view:block:powered:' . implode(':', $keys));
     $this->assertIdentical($cache_entry->tags, $expected_cache_tags);
     $expected_cache_tags = array(
@@ -395,7 +395,7 @@
       'rendered',
     );
     sort($expected_cache_tags);
-    $keys = \Drupal::service('cache_contexts_manager')->convertTokensToKeys(['languages:language_interface', 'theme', 'user.permissions']);
+    $keys = \Drupal::service('cache_contexts_manager')->convertTokensToKeys(['languages:language_interface', 'theme', 'user.permissions'])->getKeys();
     $cache_entry = \Drupal::cache('render')->get('entity_view:block:powered-2:' . implode(':', $keys));
     $this->assertIdentical($cache_entry->tags, $expected_cache_tags);
 
diff -u b/core/modules/block/src/Tests/BlockViewBuilderTest.php b/core/modules/block/src/Tests/BlockViewBuilderTest.php
--- b/core/modules/block/src/Tests/BlockViewBuilderTest.php
+++ b/core/modules/block/src/Tests/BlockViewBuilderTest.php
@@ -160,7 +160,7 @@
 
     // Test that a cache entry is created.
     $build = $this->getBlockRenderArray();
-    $cid = 'entity_view:block:test_block:' . implode(':', \Drupal::service('cache_contexts_manager')->convertTokensToKeys(['languages:' . LanguageInterface::TYPE_INTERFACE, 'theme', 'user.permissions']));
+    $cid = 'entity_view:block:test_block:' . implode(':', \Drupal::service('cache_contexts_manager')->convertTokensToKeys(['languages:' . LanguageInterface::TYPE_INTERFACE, 'theme', 'user.permissions'])->getKeys());
     $this->renderer->renderRoot($build);
     $this->assertTrue($this->container->get('cache.render')->get($cid), 'The block render element has been cached.');
 
@@ -214,7 +214,7 @@
     // Advanced: cached block, but an alter hook adds an additional cache key.
     $alter_add_key = $this->randomMachineName();
     \Drupal::state()->set('block_test_view_alter_cache_key', $alter_add_key);
-    $cid = 'entity_view:block:test_block:' . $alter_add_key . ':' . implode(':', \Drupal::service('cache_contexts_manager')->convertTokensToKeys(['languages:' . LanguageInterface::TYPE_INTERFACE, 'theme', 'user.permissions']));
+    $cid = 'entity_view:block:test_block:' . $alter_add_key . ':' . implode(':', \Drupal::service('cache_contexts_manager')->convertTokensToKeys(['languages:' . LanguageInterface::TYPE_INTERFACE, 'theme', 'user.permissions'])->getKeys());
     $expected_keys = array_merge($default_keys, array($alter_add_key));
     $build = $this->getBlockRenderArray();
     $this->assertIdentical($expected_keys, $build['#cache']['keys'], 'An altered cacheable block has the expected cache keys.');