Add InternalSurfaceFlag so we know if RenderTargetProxys and RenderTargets use GL FBO 0.

Bug: skia:7748
Change-Id: I2fda3cde12ccdef19fe06ff287a8024b58d28ef0
Reviewed-on: https://skia-review.googlesource.com/124048
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
15 files changed