Unprefix webkitImageSmoothingEnabled -> imageSmoothingEnabled.

Most tests were modified to test the unprefixed version. One (canvas-imageSmoothingEnabled.html) was copied to a new name to test the prefixed version. Since the prefixed implementation is just a wrapper to the unprefixed implementation, that should be enough coverage.

BUG=
R=dglazkov@chromium.org

Review URL: https://codereview.chromium.org/20527005

git-svn-id: svn://svn.chromium.org/blink/trunk@155624 bbb929c8-8fbe-4397-9dbb-9b2b20218538