Don't resume commits after every layout.

Don't resume commits after every layout.

We were resuming tree commits after any layout on the main frame even if rendering
was not ready and we had pending sheets or imports. This means causing layout
through tasks or API calls (ex. offsetTOp) would start pumping BeginMainFrames
and running the pipeline for no reason.

FOUC is avoided in these cases by the system inside blink that uses placeholder
styles which makes content display: none for updateLayout calls. Still we may
compute the style because of an updateLayoutIgnorePendingStylesheets() call
(ex. offsetTop) and in that case FOUC is avoided because of the painting code
which paints white until sheets have loaded.

This patch removes the call to resumeTreeViewCommits in layoutUpdated, since
we'll already resume when all sheets load or if the body is inserted and there's
no pending sheets. It then adds a new client callback for when the document
finishes parsing so that we resume commits for SVG documents which will never
have a body and may not have any sheets. I can't figure out how to write a test
for this though since layout tests artificially pump frames and paint.

This eager code for resuming commits dates back to:
https://chromium.googlesource.com/chromium/blink/+/c7e01da17b036b054fc0acf2d86483f4cdcf5cc0

BUG=504126
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=200515

[esprehn, 2015-08-13 18:50:58]

The CQ bit was checked by esprehn@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-08-13 18:51:23]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1292143003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1292143003/1

[esprehn, 2015-08-13 19:58:39]

esprehn@chromium.org changed reviewers:
+ dglazkov@chromium.org, enne@chromium.org, ojan@chromium.org

[commit-bot: I haz the power, 2015-08-13 20:55:17]

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

[commit-bot: I haz the power, 2015-08-13 20:55:18]

Dry run: This issue passed the CQ dry run.

[esprehn, 2015-08-13 21:29:18]

The CQ bit was checked by esprehn@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-08-13 21:29:29]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1292143003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1292143003/20001

[esprehn, 2015-08-13 21:30:34]

esprehn@chromium.org changed reviewers:
+ bryauade@chromium.org

[esprehn, 2015-08-13 21:58:42]

esprehn@chromium.org changed reviewers:
+ trchen@chromium.org

[commit-bot: I haz the power, 2015-08-13 22:38:55]

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

[commit-bot: I haz the power, 2015-08-13 22:38:56]

Dry run: This issue passed the CQ dry run.

[esprehn, 2015-08-14 01:30:26]

Ping. This should be a great improvement. :)

[dglazkov, 2015-08-14 02:56:13]

lgtm

[esprehn, 2015-08-14 03:02:47]

The CQ bit was checked by esprehn@chromium.org

[commit-bot: I haz the power, 2015-08-14 03:02:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1292143003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1292143003/20001

[esprehn, 2015-08-14 03:04:45]

The CQ bit was unchecked by esprehn@chromium.org

[esprehn, 2015-08-14 03:05:53]

The CQ bit was checked by esprehn@chromium.org

[commit-bot: I haz the power, 2015-08-14 03:06:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1292143003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1292143003/20001

[commit-bot: I haz the power, 2015-08-14 03:09:02]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=200515

[pdr., 2015-08-15 01:04:07]

On 2015/08/14 at 03:09:02, commit-bot wrote:
> Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=200515

Is it possible to test this so we don't regress again?

[esprehn, 2015-08-15 01:05:14]

On 2015/08/15 at 01:04:07, pdr wrote:
> On 2015/08/14 at 03:09:02, commit-bot wrote:
> > Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=200515
> 
> Is it possible to test this so we don't regress again?

Probably with a unit test? I need to figure out how to control the return speed
of network resources inside a unit test. Any ideas?