[MD settings] disable clear browsing data while it is running

chrome/test/data/webui/settings/privacy_page_test.js

Index: chrome/test/data/webui/settings/privacy_page_test.js
diff --git a/chrome/test/data/webui/settings/privacy_page_test.js b/chrome/test/data/webui/settings/privacy_page_test.js
index 106e361f9568aa6d275624b792d8c3e87879c51a..5a7c863f569077d3aa51c8786f1962ef3779c20d 100644
--- a/chrome/test/data/webui/settings/privacy_page_test.js
+++ b/chrome/test/data/webui/settings/privacy_page_test.js
@@ -56,9 +56,10 @@ cr.define('settings_privacy_page', function() {
           this.clearBrowsingDataPromise_ : Promise.resolve();
     },
 
-    /** @override */
+    /** @override {!Promise} promise */
     initialize: function() {
       this.methodCalled('initialize');
+      return Promise.resolve(false);
     },
   };
 
@@ -105,6 +106,7 @@ cr.define('settings_privacy_page', function() {
         PolymerTest.clearBody();
         element = document.createElement('settings-clear-browsing-data-dialog');
         document.body.appendChild(element);
+        return testBrowserProxy.whenCalled('initialize');
       });
 
       teardown(function() { element.remove(); });