Disentangle blend mode from updateDescendantDependentFlags

Disentangle blend mode from updateDescendantDependentFlags

Instead of driving the blend mode computation from
updateDescendantDependentFlags, this CL drives the blend mode computation from
CompositingInputsUpdater. Using this approach lets us remove a bunch of
bookkeeping because CompositingInputsUpdater does all the bookkeeping for us.

Because CompositingInputsUpdater happens during the compositing update, we need
to add some code to the compositing update to run the CompositingInputsUpdater
even when compositing isn't available (e.g., SVGImage and InspectorOverlay).

R=esprehn@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=180133

[esprehn, 2014-08-13 00:27:11]

lgtm, but it won't apply?

[abarth-chromium, 2014-08-13 00:28:24]

On 2014/08/13 at 00:27:11, esprehn wrote:
> lgtm, but it won't apply?

It's based on top of https://codereview.chromium.org/468633002 which is about to
land.

[abarth-chromium, 2014-08-13 00:42:35]

The CQ bit was checked by abarth@chromium.org

[commit-bot: I haz the power, 2014-08-13 00:44:06]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/abarth@chromium.org/466193002/1

[commit-bot: I haz the power, 2014-08-13 01:49:25]

Change committed as 180133