Image changes need to push a frame on the compositor

BUG=328069
R=esprehn@chromium.org, vollick@chromium.org

Review URL: https://codereview.chromium.org/118933002

git-svn-id: svn://svn.chromium.org/blink/trunk@164199 bbb929c8-8fbe-4397-9dbb-9b2b20218538