Remove the initial space in the QUIC user agent ID.

If chrome::VersionInfo::GetVersionStringModifier() returns an empty
string (which is the case for the Stable channel and any unofficial
builds), don't append a space.

R=rtenneti@chromium.org,thestig@chromium.org
BUG=none

Review URL: https://codereview.chromium.org/420613004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@285529 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/io_thread.cc

@@ -1171,7 +1171,8 @@ void IOThread::ConfigureQuicGlobals(
 
   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);