Add logging for ScriptedAnimationController.

This is for debugging RAF based WebGL conformance tests random timeouts.

BUG=393331
TEST=bots
NOTRY=true
R=kbr@chromium.org,eseidel@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=180672

Review URL: https://codereview.chromium.org/484323002

git-svn-id: svn://svn.chromium.org/blink/trunk@180685 bbb929c8-8fbe-4397-9dbb-9b2b20218538