fix(ngAnimate): do not use event.timeStamp anymore for time tracking

Due to recent changes in Chrome, Firefox and Webkit use of the
event.timeStamp value will lead to unpredictable behaviour due to
precision changes. Therefore it's best to stick entirely to use
`Date.now()` when it comes to confirming the end of transition-
ending values. See #13494 for more info.

Applies to 1.2, 1.3, 1.4 and 1.5.

Closes #13494
Closes #13495

src/ngAnimate/animateCss.js

@@ -792,7 +792,10 @@ var $AnimateCssProvider = ['$animateProvider', function($animateProvider) {
       function onAnimationProgress(event) {
         event.stopPropagation();
         var ev = event.originalEvent || event;
-        var timeStamp = ev.$manualTimeStamp || ev.timeStamp || Date.now();
+
+        // we now always use `Date.now()` due to the recent changes with
+        // event.timeStamp in Firefox, Webkit and Chrome (see #13494 for more info)
+        var timeStamp = ev.$manualTimeStamp || Date.now();
 
         /* Firefox (or possibly just Gecko) likes to not round values up
          * when a ms measurement is used for the animation */