Add SkDocument::getStream() method.

include/core/SkDocument.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkDocument_DEFINED
 #define SkDocument_DEFINED
 
@@ skipping 104 matching lines @@
     // note: subclasses must call close() in their destructor, as the base class
     // cannot do this for them.
     virtual ~SkDocument();
 
     virtual SkCanvas* onBeginPage(SkScalar width, SkScalar height,
                                   const SkRect& content) = 0;
     virtual void onEndPage() = 0;
     virtual bool onClose(SkWStream*) = 0;
     virtual void onAbort() = 0;
 
+    // Allows subclasses to write to the stream as pages are written.
+    SkWStream* getStream() { return fStream; }
+
     enum State {
         kBetweenPages_State,
         kInPage_State,
         kClosed_State
     };
     State getState() const { return fState; }
 
 private:
     SkWStream* fStream;
     void       (*fDoneProc)(SkWStream*, bool aborted);
     State      fState;
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif