Add tracing events to track sync ipc blocker

ipc/ipc_sync_message_filter.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 "ipc/ipc_sync_message_filter.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/single_thread_task_runner.h"
@@ skipping 41 matching lines @@
     if (io_task_runner_.get()) {
       io_task_runner_->PostTask(
           FROM_HERE,
           base::Bind(&SyncMessageFilter::SendOnIOThread, this, message));
     } else {
       pending_messages_.push_back(message);
     }
   }
 
   base::WaitableEvent* events[2] = { shutdown_event_, &done_event };
-  base::WaitableEvent::WaitMany(events, 2);
+  if (base::WaitableEvent::WaitMany(events, 2) == 1) {
+    TRACE_EVENT_FLOW_END0(TRACE_DISABLED_BY_DEFAULT("ipc.flow"),
+                          "SyncMessageFilter::Send", &done_event);
+  }
 
   {
     base::AutoLock auto_lock(lock_);
     delete pending_message.deserializer;
     pending_sync_messages_.erase(&pending_message);
   }
 
   return pending_message.send_result;
 }
 
@@ skipping 23 matching lines @@
 
 bool SyncMessageFilter::OnMessageReceived(const Message& message) {
   base::AutoLock auto_lock(lock_);
   for (PendingSyncMessages::iterator iter = pending_sync_messages_.begin();
        iter != pending_sync_messages_.end(); ++iter) {
     if (SyncMessage::IsMessageReplyTo(message, (*iter)->id)) {
       if (!message.is_reply_error()) {
         (*iter)->send_result =
             (*iter)->deserializer->SerializeOutputParameters(message);
       }
+      TRACE_EVENT_FLOW_BEGIN0(TRACE_DISABLED_BY_DEFAULT("ipc.flow"),
+                              "SyncMessageFilter::OnMessageReceived",
+                              (*iter)->done_event);
       (*iter)->done_event->Signal();
       return true;
     }
   }
 
   return false;
 }
 
 SyncMessageFilter::SyncMessageFilter(base::WaitableEvent* shutdown_event,
                                      bool is_channel_send_thread_safe)
@@ skipping 19 matching lines @@
     SignalAllEvents();
   }
 
   delete message;
 }
 
 void SyncMessageFilter::SignalAllEvents() {
   lock_.AssertAcquired();
   for (PendingSyncMessages::iterator iter = pending_sync_messages_.begin();
        iter != pending_sync_messages_.end(); ++iter) {
+    TRACE_EVENT_FLOW_BEGIN0(TRACE_DISABLED_BY_DEFAULT("ipc.flow"),
+                            "SyncMessageFilter::SignalAllEvents",
+                            (*iter)->done_event);
     (*iter)->done_event->Signal();
   }
 }
 
 }  // namespace IPC