VertexArray: Cache element limit for buffer checks. 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/1150514 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>