Deflake WidgetInputMethodInteractiveTest.TwoTopWindows on Linux

Deflake WidgetInputMethodInteractiveTest.TwoTopWindows on Linux

I was able to repro the flake with ~1% probability and traced.

It was flaky because earlier window server messages were still pending
when the test started running checks. So the first `ActivateSync` would
actually break out of the message loop wait too soon.

BUG=484836
Committed: https://crrev.com/5f19016c6780aba48125ce089f00c9f0b98e8e92
Cr-Commit-Position: refs/heads/master@{#329267}

[tapted, 2015-05-11 06:35:30]

tapted@chromium.org changed reviewers:
+ sadrul@chromium.org

[tapted, 2015-05-11 06:38:46]

Hi sadrul, please take a look

[sadrul, 2015-05-11 13:51:09]

lgtm

[tapted, 2015-05-11 23:01:00]

The CQ bit was checked by tapted@chromium.org

[commit-bot: I haz the power, 2015-05-11 23:04:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1130683004/1

[commit-bot: I haz the power, 2015-05-11 23:12:03]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-11 23:13:42]

Patchset 1 (id:??) landed as
https://crrev.com/5f19016c6780aba48125ce089f00c9f0b98e8e92
Cr-Commit-Position: refs/heads/master@{#329267}