Add new public api on GrContext for computing image size.

This api will replace ComputeTextureSize.

Change-Id: I9befd8706f44250805315bdb13a559cf81c7142d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/247337
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
3 files changed