Conditionally propagate top controls update to layer tree view.

Speculative fix for null crash on a deferred closing window that then
gets its top controls state updated (code is only utilized on Android.)

Conditionally check if the layer tree view is available, like elsewhere.

R=haraken
BUG=461322

Review URL: https://codereview.chromium.org/939303006

git-svn-id: svn://svn.chromium.org/blink/trunk@190767 bbb929c8-8fbe-4397-9dbb-9b2b20218538
1 file changed