Add unpremultiply support and GM

src/pdf/SkPDFImage.h

Index: src/pdf/SkPDFImage.h
diff --git a/src/pdf/SkPDFImage.h b/src/pdf/SkPDFImage.h
index 684487f072ca40370889851626479fbbe07d0a4b..62878274fa17d5437bfc3547dbe02011fee76af1 100644
--- a/src/pdf/SkPDFImage.h
+++ b/src/pdf/SkPDFImage.h
@@ -100,6 +100,12 @@ private:
      */
     void initImageParams(bool isAlpha);
 
+    /** Initialize my bitmap field from a source bitmap. Does a deep copy
+     *  if the source is not iummutable - guarantees my copy is consistent
+     *  for the duration of its lifetime.
+     */
+    void initBitmap(const SkBitmap& bitmap);
+
     // Populate the stream dictionary.  This method returns false if
     // fSubstitute should be used.
     virtual bool populate(SkPDFCatalog* catalog);