Add fast/canvas/canvas-lost-gpu-context.html to NeverFixTests

It's only meaningful when run as part of the virtual/gpu/ test suite, and
causes test flakiness when run outside that suite.

R=junov@chromium.org
BUG=305021

Review URL: https://codereview.chromium.org/33583002

git-svn-id: svn://svn.chromium.org/blink/trunk@160159 bbb929c8-8fbe-4397-9dbb-9b2b20218538