fix($animateCss): ensure that rAF waiting loop doesn't ignore pending items during a flush

Some animations may involve multiple stages of RAF requests before they
are run. This issue may cause an animation never to fire since the rAF
waiting queue may be modified during the flush stage and the code would
only pay attention to its starting length. This fix makes the rAF
flushing loop pay attention to the length with each iteration.

Author: matsko

src/ngAnimate/animateCss.js

@@ -494,9 +494,12 @@ var $AnimateCssProvider = ['$animateProvider', function($animateProvider) {
         //WILL RESULT IN AN UNPREDICTABLE BUG THAT IS VERY HARD TO TRACK DOWN AND
         //WILL TAKE YEARS AWAY FROM YOUR LIFE.
         var width = bod.offsetWidth + 1;
-        forEach(rafWaitQueue, function(cb) {
-          cb(width);
-        });
+
+        // we use a for loop to ensure that if the queue is changed
+        // during this looping then it will consider new requests
+        for (var i = 0; i < rafWaitQueue.length; i++) {
+          rafWaitQueue[i](width);
+        }
         rafWaitQueue.length = 0;
       });
     }