Drop the event when the target window has been deleted.

In the viz-hit-test case, when we cannot find the target window in
EventTargeter, we were using NOTREACHED before this CL. But there are
cases where the target window has simply been deleted by the time this
event is processed, e.g. clicking the settings button inside system
tray's network page, mouse move events after that but before the system
tray goes away would fail. In these cases, it makes sense to just drop
the event like we did in non-viz hit-test. Kept the TODO to investigate
if it can be a security fault when no target window is found.

Also fixes a memory exception in HTQ when using the transform directly.

Bug: 752380
Change-Id: Ifa099c88a98d623b8be363fe3a77b7bc8eea4a54
Reviewed-on: https://chromium-review.googlesource.com/651564
Commit-Queue: Ria Jiang <riajiang@chromium.org>
Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501636}
4 files changed