tests(docsAppE2E): fix race condition flake with switching to new frame

Closes #7569

Author: juliemr

test/e2e/docsAppE2E.js

@@ -27,8 +27,8 @@ describe('docs.angularjs.org', function () {
     it('should show the functioning input directive example', function () {
       browser.get('index-debug.html#!/api/ng/directive/input');
 
-      //Wait for animation
-      browser.sleep(500);
+      // Ensure that the page is loaded before trying to switch frames.
+      browser.waitForAngular();
 
       browser.switchTo().frame('example-input-directive');
 
@@ -66,4 +66,4 @@ describe('docs.angularjs.org', function () {
       expect(element(by.css('.minerr-errmsg')).getText()).toEqual("Argument 'Missing' is not a function, got undefined");
     });
   });
-});
+});