test(expression): add sleep(100) to protractor spec that uses alert

In Chrome, if two alert boxes pop up, without enough time between them,
Protractor (or possibly ChromeDriver) sometimes fails to recognize the
second alert.

docs/content/guide/expression.ngdoc

@@ -141,6 +141,9 @@ provide mockable access to globals.
       }
       element(by.css('[ng-click="greet()"]')).click();
 
+      // We need to give the browser time to display the alert
+      browser.sleep(100);
+
       var alertDialog = browser.switchTo().alert();
 
       expect(alertDialog.getText()).toEqual('Hello World');