Optimize chained string concatenation in SPDY code.

net/spdy/spdy_session.cc

Index: net/spdy/spdy_session.cc
diff --git a/net/spdy/spdy_session.cc b/net/spdy/spdy_session.cc
index a6478dff29bf0421620e089515f6616cebfa3072..047ab2ff01d0617218146367f96d1f48c5dba415 100644
--- a/net/spdy/spdy_session.cc
+++ b/net/spdy/spdy_session.cc
@@ -64,9 +64,8 @@ scoped_ptr<base::ListValue> SpdyHeaderBlockToListValue(
   scoped_ptr<base::ListValue> headers_list(new base::ListValue());
   for (SpdyHeaderBlock::const_iterator it = headers.begin();
        it != headers.end(); ++it) {
-    headers_list->AppendString(
-        it->first + ": " +
-        ElideHeaderValueForNetLog(log_level, it->first, it->second));
+    headers_list->AppendString(std::string(it->first).append(": ").append(
+        ElideHeaderValueForNetLog(log_level, it->first, it->second)));
   }
   return headers_list.Pass();
 }
@@ -2535,8 +2534,9 @@ void SpdySession::OnWindowUpdate(SpdyStreamId stream_id,
       RecordProtocolErrorHistogram(PROTOCOL_ERROR_INVALID_WINDOW_UPDATE_SIZE);
       DoDrainSession(
           ERR_SPDY_PROTOCOL_ERROR,
-          "Received WINDOW_UPDATE with an invalid delta_window_size " +
-              base::UintToString(delta_window_size));
+          std::string(
+              "Received WINDOW_UPDATE with an invalid delta_window_size ")
+              .append(base::UintToString(delta_window_size)));

[mmenke, 2015/03/09 20:21:58]

This could just be:

base::StringPrintf("Received... %i", delta_window_size);

(StringPrintf may be slower, but given that this is done on errors only, I don't
think performance matters...and it may well be faster, anyways, since it creates
2 fewer std::strings)

       return;
     }
 
@@ -3147,10 +3147,12 @@ void SpdySession::IncreaseSendWindowSize(int32 delta_window_size) {
     RecordProtocolErrorHistogram(PROTOCOL_ERROR_INVALID_WINDOW_UPDATE_SIZE);
     DoDrainSession(
         ERR_SPDY_PROTOCOL_ERROR,
-        "Received WINDOW_UPDATE [delta: " +
-            base::IntToString(delta_window_size) +
-            "] for session overflows session_send_window_size_ [current: " +
-            base::IntToString(session_send_window_size_) + "]");
+        std::string("Received WINDOW_UPDATE [delta: ")
+            .append(base::IntToString(delta_window_size))
+            .append(
+                 "] for session overflows session_send_window_size_ [current: ")
+            .append(base::IntToString(session_send_window_size_))
+            .append("]"));
     return;
   }
 
@@ -3232,11 +3234,13 @@ void SpdySession::DecreaseRecvWindowSize(int32 delta_window_size) {
   // negative. If we do, the receive window isn't being respected.
   if (delta_window_size > session_recv_window_size_) {
     RecordProtocolErrorHistogram(PROTOCOL_ERROR_RECEIVE_WINDOW_VIOLATION);
-    DoDrainSession(
-        ERR_SPDY_FLOW_CONTROL_ERROR,
-        "delta_window_size is " + base::IntToString(delta_window_size) +
-            " in DecreaseRecvWindowSize, which is larger than the receive " +
-            "window size of " + base::IntToString(session_recv_window_size_));
+    DoDrainSession(ERR_SPDY_FLOW_CONTROL_ERROR,
+                   std::string("delta_window_size is ")
+                       .append(base::IntToString(delta_window_size))
+                       .append(
+                            " in DecreaseRecvWindowSize, which is larger than "
+                            "the receive window size of ")
+                       .append(base::IntToString(session_recv_window_size_)));
     return;
   }