Move canvas->surface association to the device subclasses

include/core/SkBitmapDevice.h

Index: include/core/SkBitmapDevice.h
diff --git a/include/core/SkBitmapDevice.h b/include/core/SkBitmapDevice.h
index a801420584a0f50d263dfa99ce5662ea53753ced..3593699a476199372e84fa4d2d5c914cc556fb3d 100644
--- a/include/core/SkBitmapDevice.h
+++ b/include/core/SkBitmapDevice.h
@@ -133,6 +133,11 @@ protected:
     void lockPixels() SK_OVERRIDE;
     void unlockPixels() SK_OVERRIDE;
 
+
+    /** Creates a backend bitmap for a new bitmap device.
+     * returns true on success, with compatible bitmap in \target.
+     */
+    static bool CreateBackendBitmap(const SkImageInfo& origInfo, SkBitmap* target);
 private:
     friend class SkCanvas;
     friend struct DeviceCM; //for setMatrixClip
@@ -142,11 +147,12 @@ private:
     friend class SkDeviceImageFilterProxy;
 
     friend class SkSurface_Raster;
+    friend class SkRasterDevice;
 
     // used to change the backend's pixels (and possibly config/rowbytes)
     // but cannot change the width/height, so there should be no change to
     // any clip information.
-    void replaceBitmapBackendForRasterSurface(const SkBitmap&) SK_OVERRIDE;
+    void replaceBitmapBackend(const SkBitmap&) SK_OVERRIDE;
 
     SkBaseDevice* onCreateCompatibleDevice(const CreateInfo&) SK_OVERRIDE;