JavaScript: when starting Backbone history, stop if previously started.

Prevent a potential error condition if Backbone history is started by a plugin or theme before core tries to start it. 

Props tfrommen.
Fixes #39612.


git-svn-id: https://develop.svn.wordpress.org/trunk@40076 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/js/revisions.js

@@ -411,6 +411,9 @@ window.wp = window.wp || {};
 			// Start the router if browser supports History API
 			if ( window.history && window.history.pushState ) {
 				this.router = new revisions.Router({ model: this });
+				if ( Backbone.History.started ) {
+					Backbone.history.stop();
+				}
 				Backbone.history.start({ pushState: true });
 			}
 		},

src/wp-admin/js/theme.js

@@ -1431,6 +1431,9 @@ themes.Run = {
 		this.view.render();
 		this.routes();
 
+		if ( Backbone.History.started ) {
+			Backbone.history.stop();
+		}
 		Backbone.history.start({
 			root: themes.data.settings.adminUrl,
 			pushState: true,
@@ -1884,6 +1887,9 @@ themes.RunInstaller = {
 		this.view.render();
 		this.routes();
 
+		if ( Backbone.History.started ) {
+			Backbone.history.stop();
+		}
 		Backbone.history.start({
 			root: themes.data.settings.adminUrl,
 			pushState: true,

src/wp-includes/js/media-grid.js

@@ -844,6 +844,9 @@ Manage = MediaFrame.extend({
 	startHistory: function() {
 		// Verify pushState support and activate
 		if ( window.history && window.history.pushState ) {
+			if ( Backbone.History.started ) {
+				Backbone.history.stop();
+			}
 			Backbone.history.start( {
 				root: window._wpMediaGridSettings.adminUrl,
 				pushState: true

src/wp-includes/js/media/views/frame/manage.js

@@ -259,6 +259,9 @@ Manage = MediaFrame.extend({
 	startHistory: function() {
 		// Verify pushState support and activate
 		if ( window.history && window.history.pushState ) {
+			if ( Backbone.History.started ) {
+				Backbone.history.stop();
+			}
 			Backbone.history.start( {
 				root: window._wpMediaGridSettings.adminUrl,
 				pushState: true