[sksg] Simplify ScopedRenderContext

ScopedRenderContext tries really hard to avoid unnecessary RenderContext
initializations.

This is most likely unneeded because

  a) the structure is quite lightweight

and

  b) all ScopedRenderContext instantiation sites imediately call setters
     which require a writable context (assuming no-op args are uncommon)

Let's get rid of that over-engineered gunk.

Bug: skia:
Change-Id: Ieedc20c63c66b4d43744359e881c20639654040c
Reviewed-on: https://skia-review.googlesource.com/146761
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
2 files changed