Android: Fix Favicon NPE in accessibility mode

TabFavicon is Tab's UserData which should not be accessed after
Tab is destroyed or its WebContent is not ready yet. This CL adds
the corresponding check to avoid NPE that occurs when working
in accessibility mode, which attempts to access a Tab already
destroyed after an animation effect or Tab is not loaded with
a new WebContents object.

Bug: 940332
Change-Id: If77c0eab251fb0bc728f046605a9f6930187557b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1516116
Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#639735}
1 file changed