Reduce SpdyHeaderBlock copies with move semantics.

net/spdy/spdy_session.h

Index: net/spdy/spdy_session.h
diff --git a/net/spdy/spdy_session.h b/net/spdy/spdy_session.h
index c5eb613944a8096512d8305f7102069c4e6e6b91..3fca318107bfdec97c90eae4a9421917cb2a8821 100644
--- a/net/spdy/spdy_session.h
+++ b/net/spdy/spdy_session.h
@@ -372,11 +372,10 @@ class NET_EXPORT SpdySession : public BufferedSpdyFramerVisitorInterface,
                           std::unique_ptr<SpdyBufferProducer> producer);
 
   // Creates and returns a SYN frame for |stream_id|.
-  std::unique_ptr<SpdySerializedFrame> CreateSynStream(
-      SpdyStreamId stream_id,
-      RequestPriority priority,
-      SpdyControlFlags flags,
-      const SpdyHeaderBlock& headers);
+  std::unique_ptr<SpdySerializedFrame> CreateSynStream(SpdyStreamId stream_id,
+                                                       RequestPriority priority,
+                                                       SpdyControlFlags flags,
+                                                       SpdyHeaderBlock headers);
 
   // Creates and returns a SpdyBuffer holding a data frame with the
   // given data. May return NULL if stalled by flow control.