For non-opaque SkBitmapDevices, replace malloc-then-zero with calloc.

include/core/SkMallocPixelRef.h

 /*
  * Copyright 2008 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkMallocPixelRef_DEFINED
 #define SkMallocPixelRef_DEFINED
@@ skipping 25 matching lines @@
      *  if rowBytes is invalid for the specified info.
      *
      *  This pixelref will ref() the specified colortable (if not NULL).
      *
      *  Returns NULL on failure.
      */
     static SkMallocPixelRef* NewAllocate(const SkImageInfo& info,
                                          size_t rowBytes, SkColorTable*);
 
     /**
+     *  Identical to NewAllocate, except all pixel bytes are zeroed.
+     */
+    static SkMallocPixelRef* NewZeroed(const SkImageInfo& info,
+                                       size_t rowBytes, SkColorTable*);
+
+    /**
      *  Return a new SkMallocPixelRef with the provided pixel storage,
      *  rowBytes, and optional colortable. On destruction, ReleaseProc
      *  will be called.
      *
      *  This pixelref will ref() the specified colortable (if not NULL).
      *
      *  If ReleaseProc is NULL, the pixels will never be released. This
      *  can be useful if the pixels were stack allocated. However, such an
      *  SkMallocPixelRef must not live beyond its pixels (e.g. by copying
      *  an SkBitmap pointing to it, or drawing to an SkPicture).
@@ skipping 18 matching lines @@
      */
     static SkMallocPixelRef* NewWithData(const SkImageInfo& info,
                                          size_t rowBytes,
                                          SkColorTable* ctable,
                                          SkData* data);
 
     void* getAddr() const { return fStorage; }
 
     class PRFactory : public SkPixelRefFactory {
     public:
-        virtual SkPixelRef* create(const SkImageInfo&,
-                                   size_t rowBytes,
-                                   SkColorTable*) override;
+        SkPixelRef* create(const SkImageInfo&, size_t rowBytes, SkColorTable*) override;
+    };
+
+    class ZeroedPRFactory : public SkPixelRefFactory {
+    public:
+        SkPixelRef* create(const SkImageInfo&, size_t rowBytes, SkColorTable*) override;
     };
 
 protected:
     // The ownPixels version of this constructor is deprecated.
     SkMallocPixelRef(const SkImageInfo&, void* addr, size_t rb, SkColorTable*,
                      bool ownPixels);
     virtual ~SkMallocPixelRef();
 
     bool onNewLockPixels(LockRec*) override;
     void onUnlockPixels() override;
     size_t getAllocatedSizeInBytes() const override;
 
 private:
+    // Uses alloc to implement NewAllocate or NewZeroed.
+    static SkMallocPixelRef* NewUsing(void*(*alloc)(size_t),
+                                      const SkImageInfo&,
+                                      size_t rowBytes,
+                                      SkColorTable*);
+
     void*           fStorage;
     SkColorTable*   fCTable;
     size_t          fRB;
     ReleaseProc     fReleaseProc;
     void*           fReleaseProcContext;
 
     SkMallocPixelRef(const SkImageInfo&, void* addr, size_t rb, SkColorTable*,
                      ReleaseProc proc, void* context);
 
     typedef SkPixelRef INHERITED;
 };
 
 
 #endif