Reorganize Layer Hoisting code

With the new MultiPictureDraw API the GrContext will be performing the layer hoisting (instead of the SkGpuDevice). This CL being moving the layer hoisting functionality to GrLayerHoister rather then dumping it straight into GrContext.

R=bsalomon@google.com

Author: robertphillips@google.com

Review URL: https://codereview.chromium.org/531733003
6 files changed