Stop RenderProgress timer on destruction.

To handle the Oilpan case where the RenderObject stays
around until the next GC after the object has been
destroy()ed, stop the RenderProgress animation timer.

R=tkent@chromium.org
BUG=

Review URL: https://codereview.chromium.org/476543003

git-svn-id: svn://svn.chromium.org/blink/trunk@180536 bbb929c8-8fbe-4397-9dbb-9b2b20218538