Implement SnapTransform which takes a decomposed transform and viewport
and tries to nudge the rotation, scale and translation values. It tries applying the inverse of
the transform to the viewport. (Objects in this rect having the
transform applied will end up in the viewport) If the transform maps the
corners onto integer points and the corners are no more than 1 pixel
away we will return success and the decomposed transform with the new
rotation value.

R=vollick@chromium.org
BUG=280280

Review URL: https://codereview.chromium.org/23444049

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230849 0039d316-1c4b-4281-b951-d872f2087c98