GitLab

QuickAnswersUiController should not try to access the quick answers view
in destructor, since the view is owned by view hierarchy.

Set the pointer to null instead and added a unittest case for it.

Bug: b/162806534
Test: Run the newly added test in ash_unittests
Change-Id: Iedc5ca63c178a62b54b55525d5469874e97704c0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2336495Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Yue Li <updowndota@chromium.org>
Cr-Commit-Position: refs/heads/master@{#794736}