Fix misnamed SVGHandler::canAnimateThumb()

Caused the animation warning to not be present on
image description pages

Also add unit tests. Since I'm adding an animated svg file for
this unit test, also add a metadata extraction test for animated
svgs, since we're missing one.

Change-Id: Id03e1a0e1c151d3c575a695a42c54b709187d10a
follow-up: 876128f8c9f0ce6a8424336f
Merge "Fix misnamed SVGHandler::canAnimateThumb()"