Fix and enable WebViewInteractiveTest.Focus_InputMethod

Fix and enable WebViewInteractiveTest.Focus_InputMethod

There were couple issues that were fixed:
1. If oninput listener fires before the guest is requested to "wait
for oninput", we would timeout. This is taken care of by a flag.
2. TextInputClient::SetCompositionText() call sends an IPC to the
renderer/, if the next JavaScript step runs before the IPC is sent
then that would fail the test. This is taken care of by sending
executing empty JavaScript code on the embedder.

BUG=387956
Test=Internal test only change, nothing visible.

Committed: https://crrev.com/f69da7c88e832aa7751d5756c7beff3e183e905f
Cr-Commit-Position: refs/heads/master@{#293341}

[lazyboy, 2014-09-03 23:34:15]

lazyboy@chromium.org changed reviewers:
+ fsamuel@chromium.org

[Fady Samuel, 2014-09-04 16:11:47]

lgtm

[lazyboy, 2014-09-04 16:14:03]

The CQ bit was checked by lazyboy@chromium.org

[commit-bot: I haz the power, 2014-09-04 16:16:27]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/lazyboy@chromium.org/532883003/1

[commit-bot: I haz the power, 2014-09-04 19:25:26]

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

[commit-bot: I haz the power, 2014-09-04 19:25:28]

Try jobs failed on following builders:
  win_chromium_x64_rel_swarming on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[lazyboy, 2014-09-04 19:28:54]

The CQ bit was checked by lazyboy@chromium.org

[commit-bot: I haz the power, 2014-09-04 19:30:38]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/lazyboy@chromium.org/532883003/1

[commit-bot: I haz the power, 2014-09-04 21:37:29]

Committed patchset #1 (id:1) as 92b29f34444e2a7fb2d90eea3dbc861d5336613b

[commit-bot: I haz the power, 2014-09-10 03:32:49]

Patchset 1 (id:??) landed as
https://crrev.com/f69da7c88e832aa7751d5756c7beff3e183e905f
Cr-Commit-Position: refs/heads/master@{#293341}