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

net/spdy/hpack/hpack_entry_test.cc

Index: net/spdy/hpack/hpack_entry_test.cc
diff --git a/net/spdy/hpack/hpack_entry_test.cc b/net/spdy/hpack/hpack_entry_test.cc
index eb7de1c3bd7ecca4fda959be82d14ba28deabf4d..eda78d0c73ecc95d6f866e701f7ad1568c1c5dce 100644
--- a/net/spdy/hpack/hpack_entry_test.cc
+++ b/net/spdy/hpack/hpack_entry_test.cc
@@ -4,16 +4,12 @@
 
 #include "net/spdy/hpack/hpack_entry.h"
 
-#include <string>
-
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace net {
 
 namespace {
 
-using std::string;
-
 class HpackEntryTest : public ::testing::Test {
  protected:
   HpackEntryTest()
@@ -46,7 +42,7 @@ class HpackEntryTest : public ::testing::Test {
     return name_.size() + value_.size() + HpackEntry::kSizeOverhead;
   }
 
-  string name_, value_;
+  SpdyString name_, value_;
 
  private:
   // Referenced by HpackEntry instances.