Gardening: virtual/gpu/fast/canvas/canvas-path-addpath.html is flaky

BUG=368531
TBR=jsbell

Review URL: https://codereview.chromium.org/254233002

git-svn-id: svn://svn.chromium.org/blink/trunk@172893 bbb929c8-8fbe-4397-9dbb-9b2b20218538