Keep SVGImage alive across its animation timer callback.
Keep SVGImage alive across its animation timer callback.

An SVGImage runs the risk of being finalized while its animation
callback is running. Add the required protection.

The premature finalization is only a possibility with Oilpan enabled;
see code comment.

R=haraken,fs@opera.com
BUG=340522

Review URL: https://codereview.chromium.org/891263003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@189338 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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