add pixelref->readPixels()

unimplemented (for now) on the gpu side



git-svn-id: http://skia.googlecode.com/svn/trunk@1037 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/gpu/SkGrTexturePixelRef.h b/include/gpu/SkGrTexturePixelRef.h
index 1f5133f..a423251 100644
--- a/include/gpu/SkGrTexturePixelRef.h
+++ b/include/gpu/SkGrTexturePixelRef.h
@@ -40,6 +40,7 @@
 
     // override from SkPixelRef
     virtual void onUnlockPixels() {}
+    virtual bool onReadPixels(SkBitmap* dst, const SkIRect* subset);
 
 private:
     GrTexture*  fTexture;