Compositor hit test performance improvement

Compositor hit test performance improvement

When computing touch hit rects, keep track of the rect for the parent element
in the render tree.  If a child lives in the same layer and it's rect
is entirely contained by the parent (fairly common in practice), then
we can skip it.

For the sites I've found with the most hit rects (from our main telemetry
page sets), this decreases hit rect computation time by about 20-60%.

BUG=263416
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=155344

[Rick Byers, 2013-07-23 17:20:50]

Levi,
This is the first, in what I hope is a series of perf optimizations for
compositor hit testing based on some telemetry measurements (see
http://crbug.com/263416 for details and data).

I've tried a few different things, but so far this optimization has had the most
dramatic impact.

Thanks,
   Rick

[leviw_travelin_and_unemployed, 2013-07-23 20:54:32]

lgtm

[commit-bot: I haz the power, 2013-07-23 20:55:22]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rbyers@chromium.org/19614004/1

[commit-bot: I haz the power, 2013-07-23 22:00:22]

Retried try job too often on linux_layout_rel for step(s) webkit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_layo...

[commit-bot: I haz the power, 2013-07-24 03:08:32]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rbyers@chromium.org/19614004/15001

[commit-bot: I haz the power, 2013-07-24 05:26:11]

Retried try job too often on win_layout_rel for step(s) webkit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_layout...

[commit-bot: I haz the power, 2013-07-24 15:33:42]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rbyers@chromium.org/19614004/15001

[commit-bot: I haz the power, 2013-07-24 17:24:05]

Retried try job too often on win_layout_rel for step(s) webkit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_layout...

[commit-bot: I haz the power, 2013-07-24 18:11:47]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rbyers@chromium.org/19614004/15001

[commit-bot: I haz the power, 2013-07-24 20:10:48]

Retried try job too often on win_layout_rel for step(s) webkit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_layout...

[commit-bot: I haz the power, 2013-08-01 14:37:48]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rbyers@chromium.org/19614004/35001

[commit-bot: I haz the power, 2013-08-01 16:57:56]

Change committed as 155344