Add a way to schedule generic per-frame events through Document.

Add a way to schedule generic per-frame events through Document.

Currently, there is no way to call ScriptedAnimationController::enqueuePerFrameEvent
through Document, there's only enqueueAnimationFrameEvent() which does not
ensure uniqueness, and special-case functions which do guarantee uniqueness
for special events like resize.

This will be for https://codereview.chromium.org/396283004/

BUG=375658

[haraken, 2014-07-18 01:17:25]

As commented in https://codereview.chromium.org/396283004/#msg9, let's split a
CL into pieces so that each piece is actually used and has a test case.

[esprehn, 2014-08-01 14:10:01]

On 2014/07/18 at 01:17:25, haraken wrote:
> As commented in https://codereview.chromium.org/396283004/#msg9, let's split a
CL into pieces so that each piece is actually used and has a test case.

What's the current progress of this?

[haraken, 2014-08-01 14:11:24]

On 2014/08/01 14:10:01, esprehn wrote:
> On 2014/07/18 at 01:17:25, haraken wrote:
> > As commented in https://codereview.chromium.org/396283004/#msg9, let's split
a
> CL into pieces so that each piece is actually used and has a test case.
> 
> What's the current progress of this?

We decided to not split the CL since a meaningful split is not easy. Waiting for
your comment on https://codereview.chromium.org/396283004/.