The purpose of this patch is to replace usages of gfxIntSize with
gfx::IntSize in BasicCompositor.
The new class YCbCrUtils has two methods ported from gfxUtils in thebes.
BasicCompositor now uses these methods instead of the ones in gfxUtils.
Also changed gfxIntSize to gfx::IntSize and gfxImageFormat to
gfx::SurfaceFormat.
