Return the default mime icon for playlist items that don't have a featured image in `wp_prepare_attachment_for_js()`.

See [27640].


Built from https://develop.svn.wordpress.org/trunk@27813


git-svn-id: http://core.svn.wordpress.org/trunk@27647 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Widget Customizer: Set hightlight color to blue. Same color as in [27741].

fixes #27358.
Built from https://develop.svn.wordpress.org/trunk@27814


git-svn-id: http://core.svn.wordpress.org/trunk@27648 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Introduce `pre_update_option` filter.

Filter is available in update_option() and allows to filter any option before its value is (maybe) serialized and updated.

see #27504.
props westonruter.

Built from https://develop.svn.wordpress.org/trunk@27815


git-svn-id: http://core.svn.wordpress.org/trunk@27649 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Widget Customizer: Convert static WP_Customize_Widgets class into instantiated class and merge Options_Transaction into WP_Customize_Widgets.

see #27504.
props westonruter.

Built from https://develop.svn.wordpress.org/trunk@27816


git-svn-id: http://core.svn.wordpress.org/trunk@27650 1a063a9b-81f0-0310-95a4-ce76da25c4cd
MediaElement.js: Update version for [27811]. see #27570.
Built from https://develop.svn.wordpress.org/trunk@27817


git-svn-id: http://core.svn.wordpress.org/trunk@27651 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Widget Customizer: Remove `UPDATE_WIDGET_AJAX_ACTION` and `UPDATE_WIDGET_NONCE_POST_KEY` constants.

see #27534.
Built from https://develop.svn.wordpress.org/trunk@27818


git-svn-id: http://core.svn.wordpress.org/trunk@27652 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Widget Customizer: Simplify nonces.

see #27534.
Built from https://develop.svn.wordpress.org/trunk@27819


git-svn-id: http://core.svn.wordpress.org/trunk@27653 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Widget Customizer: Simplify conditions in setup_widget_addition_previews().

see #27534.
Built from https://develop.svn.wordpress.org/trunk@27820


git-svn-id: http://core.svn.wordpress.org/trunk@27654 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Allow the fullscreen editor's content area to also be responsive. props avryl. fixes #27569.

Built from https://develop.svn.wordpress.org/trunk@27821


git-svn-id: http://core.svn.wordpress.org/trunk@27655 1a063a9b-81f0-0310-95a4-ce76da25c4cd