Only force BackgroundGradientView to redraw when focus changes

Only recursively call setNeedsDisplay on a BackgroundGradientView and its
descendants when the focus of the view's parent window changes. Prior to
this change setNeedsDisplay would be called even if the view's parent
window did not change its focus (but rather, some other window had its
focus changed).

This substantially speeds up new window and tab switch time.

BUG=351201
NOTRY=True

Review URL: https://codereview.chromium.org/196933002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256771 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256771