Rebaseline virtual/gpu/fast/canvas/canvas-draw-canvas-on-canvas-shadow.html

It failed since r156865, and the new result looks better.

BUG=
TBR=junov@chromium.org

Review URL: https://codereview.chromium.org/23561003

git-svn-id: svn://svn.chromium.org/blink/trunk@156887 bbb929c8-8fbe-4397-9dbb-9b2b20218538