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

net/spdy/platform/api/spdy_string_utils.h

Index: net/spdy/platform/api/spdy_string_utils.h
diff --git a/net/spdy/platform/api/spdy_string_utils.h b/net/spdy/platform/api/spdy_string_utils.h
index 3d7da08b7f79f993f153311d8bf5b08f17946870..4f986ff2fb02539f7addf4b5ca47076fce486789 100644
--- a/net/spdy/platform/api/spdy_string_utils.h
+++ b/net/spdy/platform/api/spdy_string_utils.h
@@ -5,25 +5,25 @@
 #ifndef NET_SPDY_PLATFORM_API_SPDY_STRING_UTILS_H_
 #define NET_SPDY_PLATFORM_API_SPDY_STRING_UTILS_H_
 
-#include <string>
 #include <utility>
 
+#include "net/spdy/platform/api/spdy_string.h"
 #include "net/spdy/platform/impl/spdy_string_utils_impl.h"
 
 namespace net {
 
 template <typename... Args>
-inline std::string SpdyStrCat(const Args&... args) {
+inline SpdyString SpdyStrCat(const Args&... args) {
   return SpdyStrCatImpl(std::forward<const Args&>(args)...);
 }
 
 template <typename... Args>
-inline void SpdyStrAppend(std::string* output, const Args&... args) {
+inline void SpdyStrAppend(SpdyString* output, const Args&... args) {
   SpdyStrAppendImpl(output, std::forward<const Args&>(args)...);
 }
 
 template <typename... Args>
-inline std::string SpdyStringPrintf(const Args&... args) {
+inline SpdyString SpdyStringPrintf(const Args&... args) {
   return SpdyStringPrintfImpl(std::forward<const Args&>(args)...);
 }