Customize: Prevent syncing unmodified settings from controls into preview to guard against triggering an infinite reload due to selective refresh fallback behavior.

If a value is sanitized in PHP and differs from the JS value in the pane, a `change` event for the setting is triggered upon refresh. This should be avoided since the value just came from the server as being sanitized. This also fixes periodic issue where selective refresh happens immediately after a full refresh.

Fixes #37032.

Built from https://develop.svn.wordpress.org/trunk@39112


git-svn-id: http://core.svn.wordpress.org/trunk@39054 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/js/customize-controls.js

@@ -4299,6 +4299,7 @@
 			var previewer = this, synced = {}, constructs;
 
 			synced.settings = api.get();
+			synced['settings-modified-while-loading'] = previewer.settingsModifiedWhileLoading;
 			if ( 'resolved' !== previewer.deferred.active.state() || previewer.loading ) {
 				synced.scroll = previewer.scroll;
 			}
@@ -4421,7 +4422,7 @@
 		 * Refresh the preview seamlessly.
 		 */
 		refresh: function() {
-			var previewer = this;
+			var previewer = this, onSettingChange;
 
 			// Display loading indicator
 			previewer.send( 'loading-initiated' );
@@ -4435,6 +4436,15 @@
 				container:  previewer.container
 			});
 
+			previewer.settingsModifiedWhileLoading = {};
+			onSettingChange = function( setting ) {
+				previewer.settingsModifiedWhileLoading[ setting.id ] = true;
+			};
+			api.bind( 'change', onSettingChange );
+			previewer.loading.always( function() {
+				api.unbind( 'change', onSettingChange );
+			} );
+
 			previewer.loading.done( function( readyData ) {
 				var loadingFrame = this, previousPreview, onceSynced;