[Cronet iOS] Add base::StatisticsRecorder::IsActive() check

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 107 matching lines @@
   if (!g_at_exit_)
     g_at_exit_ = new base::AtExitManager;
 
   base::TaskScheduler::CreateAndSetSimpleTaskScheduler("CronetIos");
 
   url::Initialize();
   base::CommandLine::Init(0, nullptr);
 
   // Without doing this, StatisticsRecorder::FactoryGet() leaks one histogram
   // per call after the first for a given name.
   base::StatisticsRecorder::Initialize();

[xunjieli, 2017/04/06 21:37:29]

We are calling base::StatisticsRecorder::Initialize() here

[mef, 2017/04/06 22:08:11]

I wonder whether it should happen after message loop is created? WDYT?

 
   // Create a message loop on the UI thread.
   DCHECK(!base::MessageLoop::current());
   DCHECK(!g_main_message_loop);
   g_main_message_loop = new base::MessageLoopForUI();
   base::MessageLoopForUI::current()->Attach();
   // The network change notifier must be initialized so that registered
   // delegates will receive callbacks.
   DCHECK(!g_network_change_notifier);
   g_network_change_notifier = net::NetworkChangeNotifier::Create();
@@ skipping 203 matching lines @@
   const net::HttpUserAgentSettings* user_agent_settings =
       main_context_->http_user_agent_settings();
   if (!user_agent_settings) {
     return nullptr;
   }
 
   return user_agent_settings->GetUserAgent();
 }
 
 std::vector<uint8_t> CronetEnvironment::GetHistogramDeltas() {
-  base::StatisticsRecorder::Initialize();
+  DCHECK(base::StatisticsRecorder::IsActive());

[mef, 2017/04/06 22:08:11]

What would happen if they call this on background thread before init completes?

[xunjieli, 2017/04/06 23:58:01]

Is there an entry point  (if not CronetEnvironment::Initialize()) which
guarantees to complete before GetHistogramDeltas() is called?
On Android, we are doing StatisticsRecorder::Initialize() in JNIOnload() which
guarantees to be called before the user could do
CronetEngine.GetHistogramDeltas().

   std::vector<uint8_t> data;
   if (!HistogramManager::GetInstance()->GetDeltas(&data))
     return std::vector<uint8_t>();
   return data;
 }
 
 void CronetEnvironment::SetHostResolverRules(const std::string& rules) {
   base::WaitableEvent event(base::WaitableEvent::ResetPolicy::AUTOMATIC,
                             base::WaitableEvent::InitialState::NOT_SIGNALED);
   PostToNetworkThread(
@@ skipping 11 matching lines @@
   event->Signal();
 }
 
 std::string CronetEnvironment::getDefaultQuicUserAgentId() const {
   return base::SysNSStringToUTF8([[NSBundle mainBundle]
              objectForInfoDictionaryKey:@"CFBundleDisplayName"]) +
          " Cronet/" + CRONET_VERSION;
 }
 
 }  // namespace cronet