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

net/spdy/spdy_stream.h

Index: net/spdy/spdy_stream.h
diff --git a/net/spdy/spdy_stream.h b/net/spdy/spdy_stream.h
index b3d3245830e95a7a2316d1187cd14a08dbc41755..a18a7fdf0b5747550150ff0b182a8e51106841f2 100644
--- a/net/spdy/spdy_stream.h
+++ b/net/spdy/spdy_stream.h
@@ -10,7 +10,6 @@
 
 #include <deque>
 #include <memory>
-#include <string>
 #include <vector>
 
 #include "base/macros.h"
@@ -23,6 +22,7 @@
 #include "net/log/net_log_with_source.h"
 #include "net/socket/next_proto.h"
 #include "net/socket/ssl_client_socket.h"
+#include "net/spdy/platform/api/spdy_string.h"
 #include "net/spdy/spdy_buffer.h"
 #include "net/spdy/spdy_framer.h"
 #include "net/spdy/spdy_header_block.h"
@@ -289,7 +289,7 @@ class NET_EXPORT_PRIVATE SpdyStream {
   void OnClose(int status);
 
   // Called by the SpdySession to log stream related errors.
-  void LogStreamError(int status, const std::string& description);
+  void LogStreamError(int status, const SpdyString& description);
 
   // If this stream is active, reset it, and close it otherwise. In
   // either case the stream is deleted.
@@ -435,7 +435,7 @@ class NET_EXPORT_PRIVATE SpdyStream {
   // OnHeadersReceived() on the delegate if attached.
   void SaveResponseHeaders(const SpdyHeaderBlock& response_headers);
 
-  static std::string DescribeState(State state);
+  static SpdyString DescribeState(State state);
 
   const SpdyStreamType type_;