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/ops/GrClearOp.h b/src/gpu/ops/GrClearOp.h
index 57d081e..a706974 100644
--- a/src/gpu/ops/GrClearOp.h
+++ b/src/gpu/ops/GrClearOp.h
@@ -45,7 +45,7 @@
 
     CombineResult onCombineIfPossible(GrOp* t, SkArenaAlloc*, const GrCaps& caps) override;
 
-    void onPrePrepare(GrRecordingContext*, const GrSurfaceProxyView* writeView, GrAppliedClip*,
+    void onPrePrepare(GrRecordingContext*, const GrSurfaceProxyView& writeView, GrAppliedClip*,
                       const GrXferProcessor::DstProxyView&,
                       GrXferBarrierFlags renderPassXferBarriers) override {}