Flush the pending input ack when the RenderWidget is hidden

Flush the pending input ack when the RenderWidget is hidden

A throttled ack will be held until the commit, which may not happen if
the widget is hidden. Flush the ack when widget visibility changes,
ensuring the browser process gets a timely ack.

BUG=436379
Committed: https://crrev.com/8fac9d101f18be0e719477e27efb54cbde826546
Cr-Commit-Position: refs/heads/master@{#309324}

[jdduke (slow), 2014-12-20 01:49:38]

jdduke@chromium.org changed reviewers:
+ piman@chromium.org

[jdduke (slow), 2014-12-20 01:49:38]

piman@: PTAL. This may not be the right fix, but I'd like to get it live to see
if this addresses the issue. Ultimately I'd like to remove all of the ack
throttling logic, as it's really brittle...

[jdduke (slow), 2014-12-20 01:49:39]

piman@: PTAL. This may not be the right fix, but I'd like to get it live to see
if this addresses the issue. Ultimately I'd like to remove all of the ack
throttling logic, as it's really brittle...

[piman, 2014-12-20 01:49:45]

lgtm

[jdduke (slow), 2014-12-20 01:50:13]

The CQ bit was checked by jdduke@chromium.org

[commit-bot: I haz the power, 2014-12-20 01:51:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/820843002/1

[commit-bot: I haz the power, 2014-12-20 02:40:40]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-20 02:41:46]

Patchset 1 (id:??) landed as
https://crrev.com/8fac9d101f18be0e719477e27efb54cbde826546
Cr-Commit-Position: refs/heads/master@{#309324}