Merge 159961 "Defer the real work in updateCompositingLayers unt..."

Merge 159961 "Defer the real work in updateCompositingLayers unt..."

> Defer the real work in updateCompositingLayers until it's really needed.
> 
> Many types of change on a web page end up requiring that
> compositing state gets updated. Currently this work is performed
> immediately after layout, recalcStyle, and other entry points.
> 
> However, this work may happen surprisingly many times per actual
> rendered frame, which is absolutely wasteful - nothing except the
> most recent compositing state will matter when the frame finally
> gets drawn. So, instead we can defer all compositing update work
> until the compositor is ready to ask for updated compositing state.
> 
> BUG=229679, 302726
> R=jamesr@chromium.org, vollick@chromium.org
> 
> Review URL: https://codereview.chromium.org/26110004

TBR=shawnsingh@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=159993

[kareng, 2013-10-19 04:08:12]

Committed patchset #1 manually as r159993.