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

net/spdy/spdy_pinnable_buffer_piece_test.cc

Index: net/spdy/spdy_pinnable_buffer_piece_test.cc
diff --git a/net/spdy/spdy_pinnable_buffer_piece_test.cc b/net/spdy/spdy_pinnable_buffer_piece_test.cc
index ab117a2efc800d88631fe63e839abcc182a7b829..e4687eee9d887b8c09fd689673ed66e96f545b6a 100644
--- a/net/spdy/spdy_pinnable_buffer_piece_test.cc
+++ b/net/spdy/spdy_pinnable_buffer_piece_test.cc
@@ -4,6 +4,7 @@
 
 #include "net/spdy/spdy_pinnable_buffer_piece.h"
 
+#include "net/spdy/platform/api/spdy_string.h"
 #include "net/spdy/spdy_prefixed_buffer_reader.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -13,14 +14,14 @@ namespace test {
 
 class SpdyPinnableBufferPieceTest : public ::testing::Test {
  protected:
-  SpdyPrefixedBufferReader Build(const std::string& prefix,
-                                 const std::string& suffix) {
+  SpdyPrefixedBufferReader Build(const SpdyString& prefix,
+                                 const SpdyString& suffix) {
     prefix_ = prefix;
     suffix_ = suffix;
     return SpdyPrefixedBufferReader(prefix_.data(), prefix_.length(),
                                     suffix_.data(), suffix_.length());
   }
-  std::string prefix_, suffix_;
+  SpdyString prefix_, suffix_;
 };
 
 TEST_F(SpdyPinnableBufferPieceTest, Pin) {