Optionally clear PlatformCanvas instances.

skia/ext/bitmap_platform_device_mac.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "skia/ext/bitmap_platform_device_mac.h"
 
 #import <ApplicationServices/ApplicationServices.h>
 #include <time.h>
 
 #include "base/mac/mac_util.h"
@@ skipping 107 matching lines @@
   bitmap.setConfig(SkBitmap::kARGB_8888_Config, width, height);
   if (bitmap.allocPixels() != true)
     return NULL;
 
   void* data = NULL;
   if (context) {
     data = CGBitmapContextGetData(context);
     bitmap.setPixels(data);
   } else {
     data = bitmap.getPixels();
-
-    // Note: The Windows implementation clears the Bitmap later on.
-    // This bears mentioning since removal of this line makes the
-    // unit tests only fail periodically (or when MallocPreScribble is set).
-    bitmap.eraseARGB(0, 0, 0, 0);
   }
 
   bitmap.setIsOpaque(is_opaque);
 
   // If we were given data, then don't clobber it!
 #ifndef NDEBUG
   if (!context && is_opaque) {
     // To aid in finding bugs, we set the background color to something
     // obviously wrong so it will be noticable when it is not cleared
     bitmap.eraseARGB(255, 0, 255, 128);  // bright bluish green
@@ skipping 92 matching lines @@
 
 const SkBitmap& BitmapPlatformDevice::onAccessBitmap(SkBitmap* bitmap) {
   // Not needed in CoreGraphics
   return *bitmap;
 }
 
 SkDevice* BitmapPlatformDevice::onCreateCompatibleDevice(
     SkBitmap::Config config, int width, int height, bool isOpaque,
     Usage /*usage*/) {
   SkASSERT(config == SkBitmap::kARGB_8888_Config);
-  return BitmapPlatformDevice::Create(NULL, width, height, isOpaque);
+  SkDevice* bitmap_device = BitmapPlatformDevice::Create(NULL, width, height,
+                                                         isOpaque);
+  bitmap_device->accessBitmap(true).eraseARGB(0, 0, 0, 0);
+  return bitmap_device;
 }
 
 }  // namespace skia