CompositedLayerMapping should use dirty bits for bounds update

CompositedLayerMapping should use dirty bits for bounds update

This CL teaches CompositedLayerMapping::updateCompositedBounds about the
m_needToUpdateGeometry dirty bit. Now we only update the composited bounds if
they could have possibly changed.

This CL saves 14% of the compositing update in Polymer's calculator sample app.

R=ojan@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=169762

[ojan, 2014-03-21 17:40:53]

lgtm

[commit-bot: I haz the power, 2014-03-21 17:41:01]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/abarth@chromium.org/208643002/1

[commit-bot: I haz the power, 2014-03-21 17:43:34]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-03-21 17:43:34]

Try jobs failed on following builders:
  tryserver.blink on linux_blink_dbg

[abarth-chromium, 2014-03-21 18:16:39]

The CQ bit was checked by abarth@chromium.org

[commit-bot: I haz the power, 2014-03-21 18:16:47]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/abarth@chromium.org/208643002/1

[commit-bot: I haz the power, 2014-03-21 19:22:10]

Change committed as 169762