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/GrOp.h b/src/gpu/ops/GrOp.h
index 9970426..7875a3a 100644
--- a/src/gpu/ops/GrOp.h
+++ b/src/gpu/ops/GrOp.h
@@ -208,8 +208,8 @@
      * onPrePrepare must be prepared to handle both cases (when onPrePrepare has been called
      * ahead of time and when it has not been called).
      */
-    void prePrepare(GrRecordingContext* context, GrSurfaceProxyView* dstView, GrAppliedClip* clip,
-                    const GrXferProcessor::DstProxyView& dstProxyView,
+    void prePrepare(GrRecordingContext* context, const GrSurfaceProxyView& dstView,
+                    GrAppliedClip* clip, const GrXferProcessor::DstProxyView& dstProxyView,
                     GrXferBarrierFlags renderPassXferBarriers) {
         this->onPrePrepare(context, dstView, clip, dstProxyView, renderPassXferBarriers);
     }
@@ -341,7 +341,7 @@
 
     // TODO: the parameters to onPrePrepare mirror GrOpFlushState::OpArgs - fuse the two?
     virtual void onPrePrepare(GrRecordingContext*,
-                              const GrSurfaceProxyView* writeView,
+                              const GrSurfaceProxyView& writeView,
                               GrAppliedClip*,
                               const GrXferProcessor::DstProxyView&,
                               GrXferBarrierFlags renderPassXferBarriers) = 0;