Rework how initial clearing of texture works.

1) It only applies when a texture is created, not when recycled from cache

2) It is all textures or none, not a flag GrSurfaceDesc

3) It is implemented by GrGpu clearing the texture after creation if
such a thing is supported in underlying API. Otherwise, GrResourceProvider
must provide pre-zeroed mip levels.

4) Works for MIP mapped textures (all levels without initial data are cleared)

This could cause performance regressions in WebGL until we re-add the
ability to clear using glCear() in GL. Doing that requires making the "can
clear using GrGpu" caps query be per-format. Deferring doing that until
GrPixelConfig work is farther along.

Bug: skia:6718


Change-Id: I234715b9faaf61e8b44d54464497a17cd553585d

start

Change-Id: Ib84a8c3ece010cc3164b18895107e78484cbf76b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/226977
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
22 files changed