Uses checked math in VertexAttribute updates to store an element limit.
This computes more when changing the vertex array rather than at draw
call time. There may be a performance regression for workflows such as:

loop() {
  VertexAttribPointer
  DrawArrays
}

It should improve performance in most other cases.

Bug: angleproject:1391
Change-Id: I210d666d9dae9164a1c65f70f5e2151fb4f2d86d
Reviewed-on: https://chromium-review.googlesource.com/1150514Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>