fix(ngAnimate): only buffer rAF requests within the animation runners

[matsko]

Closes #12280

Here are demos to show that this works (test in IE):

Multiple RAF Requests in Angular 1.4 (#11791)

• Pre 1.4.0 functionality (really slow on IE 11 ... this was the reason why we decided to bundle the calls into a single function): https://jsfiddle.net/oga2z7bb/3/
• Current functionality (fixed for IE 11): https://angular-development.appspot.com/raf-perf/fast/index.html
• Patched functionality (fixed for IE 11): https://angular-development.appspot.com/raf-perf/slow/index.html

Material Design $$rAF perf issue (#12280)

• Current functionality (slow): https://angular-development.appspot.com/slow-raf/slow/index.html
• Patched functionality (fast): https://angular-development.appspot.com/slow-raf/fast/index.html

[matsko]

@ThomasBurleson @AdriVanHoudt @MichhDiego this should fix the issues you guys are having.

[matsko]

@IgorMinar please review.

[IgorMinar]

why do we need the extra digest after flush? it wasn't necessary before and we digest just before flushing already.

[matsko]

So beforehand what happened was:

https://github.com/angular/angular.js/blob/master/src/ngMock/angular-mocks.js#L782

1. triggerCallbacks() issued a $$rAF.flush() internally when called.
2. triggerCallbacks() also calls $timeout.flush(0) which calls a digest somewhere down the line.

But with the changes to use $animate.flush() we end up having to do this:

1. $animate.flush() clears out the RAF for the runner.
2. $rootScope.$digest() allows for the resolved promise to flush (which can only be done after the RAF has flushed).

So we need to call RAF + digest always.

[IgorMinar]

the rest looks good. thanks!

[AdriVanHoudt]

thank you so much 👏

[matsko]

Closed with dc48aad