Add SpdyString alias for std::string in net/spdy.

net/spdy/spdy_stream_test_util.h

Index: net/spdy/spdy_stream_test_util.h
diff --git a/net/spdy/spdy_stream_test_util.h b/net/spdy/spdy_stream_test_util.h
index 86838639e7e14d1728a75f9e017f5aa0d86ccee8..4fcc99bb549bb673b600c170f4253b621c1272a0 100644
--- a/net/spdy/spdy_stream_test_util.h
+++ b/net/spdy/spdy_stream_test_util.h
@@ -64,7 +64,7 @@ class StreamDelegateBase : public SpdyStream::Delegate {
 
   // Drains all data from the underlying read queue and returns it as
   // a string.
-  std::string TakeReceivedData();
+  SpdyString TakeReceivedData();
 
   // Returns whether or not the stream is closed.
   bool StreamIsClosed() const { return !stream_.get(); }
@@ -73,7 +73,7 @@ class StreamDelegateBase : public SpdyStream::Delegate {
   // returns the stream's ID when it was open.
   SpdyStreamId stream_id() const { return stream_id_; }
 
-  std::string GetResponseHeaderValue(const std::string& name) const;
+  SpdyString GetResponseHeaderValue(const SpdyString& name) const;
   bool send_headers_completed() const { return send_headers_completed_; }
 
  protected: