fix(benchmarks): add waits for naive scrolling benchmark to ensure loading

Also, simplify selectors.

Closes angular#1706.

Author: juliemr

modules/benchmarks/e2e_test/naive_infinite_scroll_perf.ts

@@ -12,12 +12,11 @@ describe('ng2 naive infinite scroll benchmark', function() {
         url: URL,
         id: 'ng2.naive_infinite_scroll',
         work: function() {
+          browser.wait(protractor.until.elementLocated(protractor.By.css('body /deep/ #scrollDiv')),
+                       5000);
           $('#reset-btn').click();
           $('#run-btn').click();
-          browser.wait(() => {
-            return $('#done').getText().then(function() { return true; },
-                                             function() { return false; });
-          }, 10000);
+          browser.wait(protractor.until.elementLocated(protractor.By.css('#done')), 10000);
         },
         params: [
           {name: 'appSize', value: appSize},

modules/benchmarks/src/naive_infinite_scroll/app.ts

@@ -83,5 +83,5 @@ export class App {
 
   _locateFinishedMarker() { return DOM.querySelector(document.body, '#done'); }
 
-  _getScrollDiv() { return DOM.query('body /deep/ #testArea /deep/ #scrollDiv'); }
+  _getScrollDiv() { return DOM.query('body /deep/ #scrollDiv'); }
 }