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

net/spdy/spdy_stream_test_util.cc

Index: net/spdy/spdy_stream_test_util.cc
diff --git a/net/spdy/spdy_stream_test_util.cc b/net/spdy/spdy_stream_test_util.cc
index 35c7f107ec5d2c87bc31b8f3fb7b7c9a03c8a4ef..f55c373c3530560aaff74e27b53d5ff10ca2c4e0 100644
--- a/net/spdy/spdy_stream_test_util.cc
+++ b/net/spdy/spdy_stream_test_util.cc
@@ -93,9 +93,9 @@ int StreamDelegateBase::WaitForClose() {
   return result;
 }
 
-std::string StreamDelegateBase::TakeReceivedData() {
+SpdyString StreamDelegateBase::TakeReceivedData() {
   size_t len = received_data_queue_.GetTotalSize();
-  std::string received_data(len, '\0');
+  SpdyString received_data(len, '\0');
   if (len > 0) {
     EXPECT_EQ(len, received_data_queue_.Dequeue(
                        base::string_as_array(&received_data), len));
@@ -103,10 +103,10 @@ std::string StreamDelegateBase::TakeReceivedData() {
   return received_data;
 }
 
-std::string StreamDelegateBase::GetResponseHeaderValue(
-    const std::string& name) const {
+SpdyString StreamDelegateBase::GetResponseHeaderValue(
+    const SpdyString& name) const {
   SpdyHeaderBlock::const_iterator it = response_headers_.find(name);
-  return (it == response_headers_.end()) ? std::string()
+  return (it == response_headers_.end()) ? SpdyString()
                                          : it->second.as_string();
 }