SkBitmap::setPixelRef():  less reference churn

BUG=skia:

Change-Id: I9657e4af5fcc808f9175ff336155374ccc77999d
Reviewed-on: https://skia-review.googlesource.com/5461
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
diff --git a/tools/skdiff/skdiff_main.cpp b/tools/skdiff/skdiff_main.cpp
index b496cad..f03ccb0 100644
--- a/tools/skdiff/skdiff_main.cpp
+++ b/tools/skdiff/skdiff_main.cpp
@@ -13,6 +13,7 @@
 #include "SkOSFile.h"
 #include "SkOSPath.h"
 #include "SkStream.h"
+#include "SkPixelRef.h"
 #include "../private/SkTDArray.h"
 #include "../private/SkTSearch.h"
 
@@ -329,10 +330,10 @@
         SkASSERT(drp != nullptr);
     }
     ~AutoReleasePixels() {
-        fDrp->fBase.fBitmap.setPixelRef(nullptr);
-        fDrp->fComparison.fBitmap.setPixelRef(nullptr);
-        fDrp->fDifference.fBitmap.setPixelRef(nullptr);
-        fDrp->fWhite.fBitmap.setPixelRef(nullptr);
+        fDrp->fBase.fBitmap.setPixelRef(nullptr, 0, 0);
+        fDrp->fComparison.fBitmap.setPixelRef(nullptr, 0, 0);
+        fDrp->fDifference.fBitmap.setPixelRef(nullptr, 0, 0);
+        fDrp->fWhite.fBitmap.setPixelRef(nullptr, 0, 0);
     }
 
 private: