Switching Blink to use new Skia SkPictureRecorder API

The Skia SkPicture recording API is changing to make it clearer when the SkPicture is valid. In the new API SkPictureRecorder::endRecording returns the new SkPicture. 

This isn't landable until Skia DEPS rolls past r14171.

Review URL: https://codereview.chromium.org/232513004

git-svn-id: svn://svn.chromium.org/blink/trunk@171691 bbb929c8-8fbe-4397-9dbb-9b2b20218538