Fix plugin placeholder invalidation issue

Fix plugin placeholder invalidation issue

Blink no longer always invalidate synchronously. If an invalidation
requirement is not generated during a frame update, the blink will
schedule an animation and will issue the invalidation in the next
frame update.

webview_plugin should handle scheduleAnimation() to trigger the
next frame update. For now we call container_->invalidate() to achieve
that.

BUG=415926
Committed: https://crrev.com/e88496b3ee30a5fbb97a91a6afa6ce143036ca84
Cr-Commit-Position: refs/heads/master@{#295991}

[Xianzhu, 2014-09-19 20:26:39]

wangxianzhu@chromium.org changed reviewers:
+ bauerb@chromium.org

[Bernhard Bauer, 2014-09-21 10:45:43]

LGTM, thanks!

[Xianzhu, 2014-09-22 15:57:26]

The CQ bit was checked by wangxianzhu@chromium.org

[commit-bot: I haz the power, 2014-09-22 15:58:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/584243002/1

[commit-bot: I haz the power, 2014-09-22 16:44:53]

Committed patchset #1 (id:1) as 241e8f8f35946d3b56aa55e78965eff0a324d65f

[commit-bot: I haz the power, 2014-09-22 16:46:08]

Patchset 1 (id:??) landed as
https://crrev.com/e88496b3ee30a5fbb97a91a6afa6ce143036ca84
Cr-Commit-Position: refs/heads/master@{#295991}