add newImage API

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 8c1dfada638db398c6b645c7e0c264c54a3b470c..512c80c44beca03134cbeee92585b8c46a46e85c 100644
--- a/src/image/SkImage_Base.h
+++ b/src/image/SkImage_Base.h
@@ -59,6 +59,10 @@ public:
                                   SkShader::TileMode,
                                   const SkMatrix* localMatrix) const { return NULL; };
 
+    // newWidth > 0, newHeight > 0, subset either NULL or a proper subset of this bounds
+    virtual SkImage* onNewImage(int newWidth, int newHeight, const SkIRect* subset,
+                                SkFilterQuality) const;
+
 private:
     const SkSurfaceProps fProps;