gpu: Fix webview parent compositor crash in context loss

gpu: Fix webview parent compositor crash in context loss

Android WebView parent compositor runs a thread without an message loop,
ie MessageLoop[Proxy]::current returns null. This means any WrapCallback
will crash immediately when called.

This is a hack-ish fix to just check for this case and call through
immediately, as the client thread and the gpu thread will be the same.

BUG=

Committed: https://crrev.com/afd978c6880d94df9cd488c2e78c4bff7b9de58f
Cr-Commit-Position: refs/heads/master@{#299742}

[boliu, 2014-10-15 00:05:09]

boliu@chromium.org changed reviewers:
+ sievers@chromium.org

[boliu, 2014-10-15 00:05:09]

PTAL

[no sievers, 2014-10-15 18:04:18]

lgtm

[boliu, 2014-10-15 18:05:55]

The CQ bit was checked by boliu@chromium.org

[commit-bot: I haz the power, 2014-10-15 18:07:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/655963002/1

[commit-bot: I haz the power, 2014-10-15 19:32:04]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-15 19:32:38]

Patchset 1 (id:??) landed as
https://crrev.com/afd978c6880d94df9cd488c2e78c4bff7b9de58f
Cr-Commit-Position: refs/heads/master@{#299742}