[PDF] Remove one copy of each content stream.

Review URL: http://codereview.appspot.com/4231044

git-svn-id: http://skia.googlecode.com/svn/trunk@856 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/pdf/SkPDFDevice.h b/include/pdf/SkPDFDevice.h
index f9247a7..3e1edb7 100644
--- a/include/pdf/SkPDFDevice.h
+++ b/include/pdf/SkPDFDevice.h
@@ -132,9 +132,10 @@
      */
     SkRefPtr<SkPDFArray> getMediaBox() const;
 
-    /** Returns a string with the page contents.
+    /** Returns a SkStream with the page contents.  The caller is responsible
+        for a reference to the returned value.
      */
-    SkString content() const;
+    SkStream* content() const;
 
 private:
     int fWidth;