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

src/core/SkBitmapDevice.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapDevice.h"
 #include "SkConfig8888.h"
 #include "SkDraw.h"
+#include "SkMallocPixelRef.h"
 #include "SkMatrix.h"
 #include "SkPaint.h"
 #include "SkPath.h"
 #include "SkPixelRef.h"
 #include "SkPixmap.h"
 #include "SkShader.h"
 #include "SkSurface.h"
 #include "SkXfermode.h"
 
 class SkColorTable;
@@ skipping 66 matching lines @@
         return nullptr;
     }
 
     const SkImageInfo info = origInfo.makeAlphaType(newAT);
     SkBitmap bitmap;
 
     if (kUnknown_SkColorType == info.colorType()) {
         if (!bitmap.setInfo(info)) {
             return nullptr;
         }
-    } else {
+    } else if (bitmap.info().isOpaque()) {
+        // If this bitmap is opaque, we don't have any sensible default color,
+        // so we just return uninitialized pixels.
         if (!bitmap.tryAllocPixels(info)) {
             return nullptr;
         }
-        if (!bitmap.info().isOpaque()) {
-            bitmap.eraseColor(SK_ColorTRANSPARENT);
+    } else {
+        // This bitmap has transparency, so we'll zero the pixels (to transparent).
+        // We use a ZeroedPRFactory as a faster alloc-then-eraseColor(SK_ColorTRANSPARENT).
+        SkMallocPixelRef::ZeroedPRFactory factory;
+        if (!bitmap.tryAllocPixels(info, &factory, nullptr/*color table*/)) {
+            return nullptr;
         }
     }
 
     return new SkBitmapDevice(bitmap, surfaceProps);
 }
 
 SkImageInfo SkBitmapDevice::imageInfo() const {
     return fBitmap.info();
 }
 
@@ skipping 267 matching lines @@
         paint.getRasterizer() ||
         paint.getPathEffect() ||
         paint.isFakeBoldText() ||
         paint.getStyle() != SkPaint::kFill_Style ||
         !SkXfermode::IsMode(paint.getXfermode(), SkXfermode::kSrcOver_Mode))
     {
         return true;
     }
     return false;
 }