GitLab

It is possible for a WebContents to be destroyed while it is being
activated in response to a mouse-click. Handle such case gracefully.

BUG=1040725

Change-Id: Ic73e631bf04e170bc8b1cd818da8d39f1963e006
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1994394
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#730244}