Remove the initial space in the QUIC user agent ID.

chrome/browser/io_thread.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/io_thread.h"
 
 #include <vector>
 
 #include "base/base64.h"
 #include "base/bind.h"
@@ skipping 1154 matching lines @@
 
   size_t max_packet_length = GetQuicMaxPacketLength(command_line,
                                                     quic_trial_group,
                                                     quic_trial_params);
   if (max_packet_length != 0) {
     globals->quic_max_packet_length.set(max_packet_length);
   }
 
   std::string quic_user_agent_id =
       chrome::VersionInfo::GetVersionStringModifier();
-  quic_user_agent_id.append(1, ' ');
+  if (!quic_user_agent_id.empty())
+    quic_user_agent_id.push_back(' ');
   chrome::VersionInfo version_info;
   quic_user_agent_id.append(version_info.ProductNameAndVersionForUserAgent());
   globals->quic_user_agent_id.set(quic_user_agent_id);
 
   net::QuicVersion version = GetQuicVersion(command_line, quic_trial_params);
   if (version != net::QUIC_VERSION_UNSUPPORTED) {
     net::QuicVersionVector supported_versions;
     supported_versions.push_back(version);
     globals->quic_supported_versions.set(supported_versions);
   }
@@ skipping 195 matching lines @@
   net::QuicVersionVector supported_versions = net::QuicSupportedVersions();
   for (size_t i = 0; i < supported_versions.size(); ++i) {
     net::QuicVersion version = supported_versions[i];
     if (net::QuicVersionToString(version) == quic_version) {
       return version;
     }
   }
 
   return net::QUIC_VERSION_UNSUPPORTED;
 }