Fixing display list 2d canvases to handle non-animated canvases

This change prevents non-animated canvases from falling back to
main thread rasterization mode. The stategy is to recycle the
SkPicture from the previous frame when there have been no draws
since the previous frame.

BUG=392612
TEST=blink platform unit test RecordingImageBufferSurfaceTest

Review URL: https://codereview.chromium.org/420453002

git-svn-id: svn://svn.chromium.org/blink/trunk@178866 bbb929c8-8fbe-4397-9dbb-9b2b20218538