Centralize computation of GrRenderTarget & GrTexture VRAM consumption

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4310

Change-Id: I676749ecf1e489f825799b619a15a45fc7dcd219
Reviewed-on: https://skia-review.googlesource.com/4310
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
11 files changed