Make SkPicture/SkImageGenerator default to SkCodec

include/core/SkPicture.h

Index: include/core/SkPicture.h
diff --git a/include/core/SkPicture.h b/include/core/SkPicture.h
index 720747e9a3232eeb9b07931b1ad1e939f489e511..d606a1ed63f9d60eb123649cddb9ffb1e952d635 100644
--- a/include/core/SkPicture.h
+++ b/include/core/SkPicture.h
@@ -54,8 +54,15 @@ public:
      *  @return A new SkPicture representing the serialized data, or NULL if the stream is
      *          invalid.
      */
-    static SkPicture* CreateFromStream(SkStream*,
-                                       InstallPixelRefProc proc = &SkImageDecoder::DecodeMemory);
+    static SkPicture* CreateFromStream(SkStream*, InstallPixelRefProc proc);
+
+    /**
+     *  Recreate a picture that was serialized into a stream.

[scroggo, 2016/02/09 16:12:17]

Should I include a comment alluding to how we'll decode any encoded images?

[reed1, 2016/02/09 20:46:26]

Sure. Something like...?

Serialized images will be passed to SkImage::NewFromData() or its equivalent

[scroggo, 2016/02/09 21:07:14]

Done - used SkIMageGenerator::NewFromEncoded, which is what we use today (and is
used by SkImage::NewFromData).

+     *  @param SkStream Serialized picture data. Ownership is unchanged by this call.
+     *  @return A new SkPicture representing the serialized data, or NULL if the stream is
+     *          invalid.
+     */
+    static SkPicture* CreateFromStream(SkStream*);
 
     /**
      *  Recreate a picture that was serialized into a buffer. If the creation requires bitmap