Pass the writeView as a const-ref instead of a pointer …

The important part is in GrOpFlushState.h were previously
we were taking a mutable pointer to the view, which should
at least be a const pointer and was making us do funky things
in some of the calling code. But I decided to go all the way
and do a const ref instead which is The Way It Should Be (tm).

Change-Id: I399d102e8b5e0a5059168cc450ae66f12ad47e13
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/336451
Reviewed-by: Greg Daniel <egdaniel@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Adlai Holler <adlai@google.com>
diff --git a/src/gpu/mock/GrMockOpTarget.h b/src/gpu/mock/GrMockOpTarget.h
index 0fa1775..7a8be01 100644
--- a/src/gpu/mock/GrMockOpTarget.h
+++ b/src/gpu/mock/GrMockOpTarget.h
@@ -82,7 +82,7 @@
     UNIMPL(uint16_t* makeIndexSpaceAtLeast(int, int, sk_sp<const GrBuffer>*, int*, int*))
     UNIMPL(void putBackIndices(int))
     UNIMPL(GrRenderTargetProxy* proxy() const)
-    UNIMPL(const GrSurfaceProxyView* writeView() const)
+    UNIMPL(const GrSurfaceProxyView& writeView() const)
     UNIMPL(const GrAppliedClip* appliedClip() const)
     UNIMPL(GrStrikeCache* strikeCache() const)
     UNIMPL(GrAtlasManager* atlasManager() const)