Create GrOptDrawState directly in the cmd buffer in GrIODB.

Review URL: https://codereview.chromium.org/746243002
Cleanup of S32_D565_Opaque_SSE2()

BUG=skia:

Review URL: https://codereview.chromium.org/725693003
Use scratch keys for stencil buffers.

BUG=skia:2889

Review URL: https://codereview.chromium.org/747043004
Add gpu support for Apple specific 'Vertex Arrays' functions

BUG=skia:

Review URL: https://codereview.chromium.org/754653002