Bug 959123 - Implement CairoImage::GetAsSourceSurface. r=nical

Deprecate CairoImage::Data::mSurface and add an mSourceSurface.
Also change all the callers of CairoImage::SetData to set the
SourceSurface as well.

Also change scope of CairoImage::mSource to private
Bug 959124 - Implement RemoteBitmapImage::GetAsSourceSurface. r=nical

Just added a subclass specific implementation of GetAsSourceSurface.
Bug 959527 - Implement SharedRGBImage::GetAsSourceSurface. r=nical