use SkImageInfo directly, instead of converting to SkBitmap::Config

include/core/SkSurface.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkSurface_DEFINED
 #define SkSurface_DEFINED
 
@@ skipping 135 matching lines @@
      *  Thought the caller could get a snapshot image explicitly, and draw that,
      *  it seems that directly drawing a surface into another canvas might be
      *  a common pattern, and that we could possibly be more efficient, since
      *  we'd know that the "snapshot" need only live until we've handed it off
      *  to the canvas.
      */
     void draw(SkCanvas*, SkScalar x, SkScalar y, const SkPaint*);
 
 protected:
     SkSurface(int width, int height);
+    SkSurface(const SkImageInfo&);
 
     // called by subclass if their contents have changed
     void dirtyGenerationID() {
         fGenerationID = 0;
     }
 
 private:
     const int   fWidth;
     const int   fHeight;
     uint32_t    fGenerationID;
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif