GitLab

Added a windows destruction observer. It is use to observe
(detect) when an Aura Window or RenderWidgetHostViewAura is
deleted during execution of a member function because of
activation/focus change.

This fixes browser crashes when exiting fullscreen Flash with ESC.

BUG=197023
TEST=Press ESC when in full-screen Flash

Review URL: https://chromiumcodereview.appspot.com/12929002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@189308 0039d316-1c4b-4281-b951-d872f2087c98