[cronet] Add member for QUIC user agent ID, with getter and setter.

components/cronet/ios/cronet_environment.mm

 // Copyright 2016 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 "components/cronet/ios/cronet_environment.h"
 
 #include <utility>
 
 #include "base/at_exit.h"
 #include "base/atomicops.h"
@@ skipping 252 matching lines @@
   if (user_agent_partial_)
     user_agent_ = web::BuildUserAgentFromProduct(user_agent_);
 
   // Cache
   base::FilePath cache_path;
   if (!PathService::Get(base::DIR_CACHE, &cache_path))
     return;
   cache_path = cache_path.Append(FILE_PATH_LITERAL("cronet"));
 
   std::unique_ptr<URLRequestContextConfig> config(new URLRequestContextConfig(
-      quic_enabled_,                  // Enable QUIC.
-      "",                             // QUIC User Agent ID.
+      quic_enabled_,  // Enable QUIC.
+      quic_enabled_ && !quic_user_agent_id_.size()

[mef, 2016/12/13 20:46:43]

nit: !quic_user_agent_id_.size() => quic_user_agent_id_.empty()

+          ? getDefaultQuicUserAgentId()
+          : quic_user_agent_id_,      // QUIC User Agent ID.

[mef, 2016/12/13 20:46:43]

Maybe move it into explicit if (...) construction above, as I'm not sure about
proper formatting for this.

I can't find explicit guideline not to use this construct, do you see it used
elsewhere?

[lilyhoughton, 2016/12/14 18:32:15]

It's used for basically the same thing in the android CL  (in the
getDefaultQuicUserId() function)

This is the formatting that cl format generated.

       http2_enabled_,                 // Enable SPDY.
       false,                          // Enable SDCH
       URLRequestContextConfig::DISK,  // Type of http cache.
       0,                              // Max size of http cache in bytes.
       false,                          // Disable caching for HTTP responses.
       cache_path.value(),  // Storage path for http cache and cookie storage.
       user_agent_,         // User-Agent request header field.
       "{}",                // JSON encoded experimental options.
       "",                  // Data reduction proxy key.
       "",                  // Data reduction proxy.
@@ skipping 66 matching lines @@
 }
 
 void CronetEnvironment::SetHostResolverRulesOnNetworkThread(
     const std::string& rules,
     base::WaitableEvent* event) {
   static_cast<net::MappedHostResolver*>(main_context_->host_resolver())
       ->SetRulesFromString(rules);
   event->Signal();
 }
 
+std::string CronetEnvironment::getDefaultQuicUserAgentId() {
+  return base::SysNSStringToUTF8([[NSBundle mainBundle]
+             objectForInfoDictionaryKey:@"CFBundleDisplayName"]) +
+         " Cronet/" + CRONET_VERSION;
+}
+
 }  // namespace cronet