Optionally clear PlatformCanvas instances.

skia/ext/bitmap_platform_device_android.h

Index: skia/ext/bitmap_platform_device_android.h
===================================================================
--- skia/ext/bitmap_platform_device_android.h	(revision 127021)
+++ skia/ext/bitmap_platform_device_android.h	(working copy)
@@ -20,9 +20,18 @@
 // -----------------------------------------------------------------------------
 class BitmapPlatformDevice : public PlatformDevice, public SkDevice {
  public:
+  // Construct a BitmapPlatformDevice. |is_opaque| should be set if the caller
+  // knows the bitmap will be completely opaque and allows some optimizations.
+  // The bitmap is not initialized.
   static BitmapPlatformDevice* Create(int width, int height, bool is_opaque);
 
-  // This doesn't take ownership of |data|
+  // Construct a BitmapPlatformDevice, as above.
+  // If |is_opaque| is false, the bitmap is initialized to 0.
+  static BitmapPlatformDevice* CreateAndClear(int width, int height,
+                                              bool is_opaque);
+
+  // This doesn't take ownership of |data|. If |data| is null, the bitmap
+  // is not initialized to 0.
   static BitmapPlatformDevice* Create(int width, int height, bool is_opaque,
                                       uint8_t* data);