skia/ext: Clip lazy pixel refs to canvas.

This patch clips lazy pixel refs to the canvas. There are
situations where we get a very large rect, which can
cause problems for the clients that don't expend a rect
larger than the recording canvas.

BUG=288777

Review URL: https://codereview.chromium.org/28903004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229702 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229702