Rename Views method get_default_argument() to getDefaultArgument()

Working on it!

• Replaced all instances of get_default_argument() with getDefaultArgument() in views, including the tests.
• Ran simpletest with all tests passing (see attached screenshot)

The patch in #2 did not take into account instances of get_default_argument() used outside of the views module. After grepping the whole site, another example was located in core/modules/user/lib/Drupal/user/Tests/Views/ArgumentDefaultTest.php. This updated patch includes the conversion to getDefaultArgument for this too.

#3: 8.x-rename-views-method-2002900-3.patch queued for re-testing.

Just realised that I need to add the public modifier before function getDefaultArgument() to adhere to OOP standards, so I'll get cracking with that.

This version includes the public modifier before function getDefaultArgument() in core/modules/views/lib/Drupal/views/Plugin/views/argument/ArgumentPluginBase.php.

+++ b/core/modules/views/lib/Drupal/views/Plugin/views/argument/Date.phpundefined
@@ -57,7 +57,7 @@ function default_argument_form(&$form, &$form_state) {
+  function getDefaultArgument($raw = FALSE) {

Add public access modifier in front of the function to adhere to the new OOP standards.

I started over again, this time remembering to add the public access modifier in front of the function.

Updating status to needs review

Cool.

Committed 0449064 and pushed to 8.x. Thanks!