Add a disabler for gathering debug compositing info from FrameView (this code
is only executed in about:tracing).
BUG=366669

Review URL: https://codereview.chromium.org/335273007

git-svn-id: svn://svn.chromium.org/blink/trunk@176766 bbb929c8-8fbe-4397-9dbb-9b2b20218538