Don't crash if there is no local main frame on WebView::handleInputEvent

Don't crash if there is no local main frame on WebView::handleInputEvent

I'm pretty sure this indicates a bug in some other part of the event
handling/routing code, but we're still sorting out those bits for OOPI.
Eventually this should be an assert.

BUG=475003
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=194321

[dcheng, 2015-04-23 18:50:35]

dcheng@chromium.org changed reviewers:
+ kenrb@chromium.org, rbyers@chromium.org

[dcheng, 2015-04-23 18:50:35]

Note: I'm not /really/ sure how we end up in this state, but it's pretty easy to
do so with the repro in the linked bug. This is a prerequisite for landing
https://codereview.chromium.org/1106673002, which makes this happen more often?

[Rick Byers, 2015-04-23 19:40:05]

I know the OOPIF input routing stuff is still in a lot of flux, so I'm OK with
this as a temporary workaround while you guys get it figured out.  LGTM.

[kenrb, 2015-04-23 20:14:34]

It certainly indicates a bug for WebViewImpl to be getting input events without
local main frame. We might want to file a new one after the crash is resolved.

lgtm

[dcheng, 2015-04-23 20:16:17]

The CQ bit was checked by dcheng@chromium.org

[commit-bot: I haz the power, 2015-04-23 20:17:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1079973007/1

[commit-bot: I haz the power, 2015-04-23 20:20:46]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=194321