Move GrRenderTargetPriv::maxWindowRectangles to GrRenderTargetContextPriv & GrRenderTargetProxy

This removes a reason to call accessRenderTarget on the GrRenderTargetContext

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4583

Change-Id: I6e8a53ffd5c1fea80f542b70e05744e2991f70f8
Reviewed-on: https://skia-review.googlesource.com/4583
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
9 files changed