Optionally clear PlatformCanvas instances.

skia/ext/bitmap_platform_device_win.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 <windows.h>
 #include <psapi.h>
 
 #include "skia/ext/bitmap_platform_device_win.h"
 
 #include "skia/ext/bitmap_platform_device_data.h"
@@ skipping 118 matching lines @@
   bitmap.setIsOpaque(is_opaque);
 
   // If we were given data, then don't clobber it!
   if (!shared_section) {
     if (is_opaque) {
 #ifndef NDEBUG
       // 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
 #endif
-    } else {
-      bitmap.eraseARGB(0, 0, 0, 0);
     }
   }
 
   // The device object will take ownership of the HBITMAP. The initial refcount
   // of the data object will be 1, which is what the constructor expects.
   return new BitmapPlatformDevice(new BitmapPlatformDeviceData(hbitmap),
                                   bitmap);
 }
 
 // static
@@ skipping 101 matching lines @@
   // operation has occurred on our DC.
   if (data_->IsBitmapDCCreated())
     GdiFlush();
   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(width, height, isOpaque, NULL);
+  SkDevice* bitmap_device = BitmapPlatformDevice::create(width, height,
+                                                         isOpaque, NULL);
+  bitmap_device->accessBitmap(true).eraseARGB(0, 0, 0, 0);
+  return bitmap_device;
 }
 
 }  // namespace skia