Optionally clear PlatformCanvas instances.

skia/ext/bitmap_platform_device_win.cc

Index: skia/ext/bitmap_platform_device_win.cc
===================================================================
--- skia/ext/bitmap_platform_device_win.cc	(revision 126450)
+++ skia/ext/bitmap_platform_device_win.cc	(working copy)
@@ -136,8 +136,6 @@
       // 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);
     }
   }
 
@@ -259,7 +257,10 @@
     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