Convert svg repaint tests to pixel test only repaint

These svg tests are really looking for their final output.  Rather than
outputting all the repaint rects (to test for over-invalidating) which
may be flaky, simply convert them to only output pixels.

BUG=345027

Review URL: https://codereview.chromium.org/205263004

git-svn-id: svn://svn.chromium.org/blink/trunk@170367 bbb929c8-8fbe-4397-9dbb-9b2b20218538