GuestView: Fix unhandled keyboard events.

GuestView: Fix unhandled keyboard events.

Unhandled keyboard events should not use the guest as source. In the case of
the OOP PDF viewer, if devtools for the guest was open, unhandled keyboard
events would go there and would be applied to the guest by devtools instead
of to the embedder. The solution is to use the embedder WebContents as the source
for the unhandled keyboard event.

BUG=450929
Committed: https://crrev.com/996d23ef2304a937dacd728fd0eeec4252d64bca
Cr-Commit-Position: refs/heads/master@{#312881}

[Fady Samuel, 2015-01-23 17:26:07]

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

[lazyboy, 2015-01-23 17:27:15]

lgtm

[Fady Samuel, 2015-01-23 17:27:38]

The CQ bit was checked by fsamuel@chromium.org

[commit-bot: I haz the power, 2015-01-23 17:27:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/872843002/1

[commit-bot: I haz the power, 2015-01-23 18:23:32]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-23 18:24:41]

Patchset 1 (id:??) landed as
https://crrev.com/996d23ef2304a937dacd728fd0eeec4252d64bca
Cr-Commit-Position: refs/heads/master@{#312881}