Connect up YUVA images for testing.

* Fixes isTextureBacked() for SkImage_GpuYUVA
* Hooks in SkImage_GpuYUVA::MakePromiseYUVATexture()
* Pass down plane texture sizes to MakePromiseYUVATexture()
* Move some other methods to SkImage_GpuBase.

Bug: skia:7901
Change-Id: I33d62c16b426abba5830f7168f9f8fd54a0cb093
Reviewed-on: https://skia-review.googlesource.com/c/161149
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
13 files changed