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

Review URL: https://codereview.chromium.org/1079973007

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@194321 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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