Allow style sharing for canvas, iframe, embed and object.

Allow style sharing for canvas, iframe, embed and object.

We didn't allow this before because they would use the layer update
hack to force a style recalc (with identical style) to make their
composited layer appear/disappear. Now we use the more modern
Element::setNeedsCompositingUpdate() which directly dirties the
compositing state without having to go through the style recalc
machinery. This means we can style share between iframes on the
page.

Committed: https://crrev.com/2f0884e24caaaa2925ef7007a5296e0fdef379cf
Cr-Commit-Position: refs/heads/master@{#354475}

[esprehn, 2015-10-16 04:08:53]

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

[commit-bot: I haz the power, 2015-10-16 04:09:01]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1405223003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1405223003/1

[esprehn, 2015-10-16 05:03:56]

esprehn@chromium.org changed reviewers:
+ dstockwell@chromium.org, ojan@chromium.org, timloh@chromium.org

[dstockwell, 2015-10-16 06:41:29]

lgtm

[commit-bot: I haz the power, 2015-10-16 07:52:25]

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

[commit-bot: I haz the power, 2015-10-16 07:52:25]

Dry run: This issue passed the CQ dry run.

[esprehn, 2015-10-16 08:39:21]

The CQ bit was checked by esprehn@chromium.org

[commit-bot: I haz the power, 2015-10-16 08:39:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1405223003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1405223003/1

[commit-bot: I haz the power, 2015-10-16 08:43:45]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-16 08:44:53]

Patchset 1 (id:??) landed as
https://crrev.com/2f0884e24caaaa2925ef7007a5296e0fdef379cf
Cr-Commit-Position: refs/heads/master@{#354475}