Fix a logic mistake calculating video compositing requirement

With overlay fullscreen video enabled, video must be composited when
fullscreen. However the opposite does not apply.

R=esprehn
BUG=262945

Review URL: https://chromiumcodereview.appspot.com/24647004

git-svn-id: svn://svn.chromium.org/blink/trunk@158359 bbb929c8-8fbe-4397-9dbb-9b2b20218538