add ways to peer into an image to get its pixels

src/image/SkImage_Base.h

Index: src/image/SkImage_Base.h
diff --git a/src/image/SkImage_Base.h b/src/image/SkImage_Base.h
index 7bd1f7e6c944f50e64ec9716189675bc6c319450..9fdfcd26770adc2e9e62b744356672f60d3c8e4b 100644
--- a/src/image/SkImage_Base.h
+++ b/src/image/SkImage_Base.h
@@ -17,6 +17,14 @@ public:
     virtual void onDraw(SkCanvas*, SkScalar x, SkScalar y, const SkPaint*) = 0;
     virtual void onDrawRectToRect(SkCanvas*, const SkRect* src,
                                   const SkRect& dst, const SkPaint*) = 0;
+
+    // Default impl calls onDraw
+    virtual bool onReadPixels(SkBitmap*, const SkIRect& subset) const;
+
+    virtual const void* onPeekPixels(SkImageInfo*, size_t* /*rowBytes*/) const {
+        return NULL;
+    }
+
     virtual GrTexture* onGetTexture() { return NULL; }
 
     // return a read-only copy of the pixels. We promise to not modify them,