Move allocation of texture from SkGpuDevice to GrLayerCache

In order to atlas the layers the GrLayerCache needs to be given more control over where a given layer's texture is allocated (i.e., it could be a raw scratch texture or in the cache).

R=bsalomon@google.com

Author: robertphillips@google.com

Review URL: https://codereview.chromium.org/350183006
5 files changed