Make flow event traces disabled-by-default, and rename "ipc" and "task" categories to "toplevel"

base/threading/worker_pool_win.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 "base/threading/worker_pool.h"
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
 #include "base/pending_task.h"
 #include "base/threading/thread_local.h"
 #include "base/tracked_objects.h"
 
 namespace base {
 
 namespace {
 
 base::LazyInstance<ThreadLocalBoolean>::Leaky
     g_worker_pool_running_on_this_thread = LAZY_INSTANCE_INITIALIZER;
 
 DWORD CALLBACK WorkItemCallback(void* param) {
   PendingTask* pending_task = static_cast<PendingTask*>(param);
-  TRACE_EVENT2("task", "WorkItemCallback::Run",
+  TRACE_EVENT2("toplevel", "WorkItemCallback::Run",
                "src_file", pending_task->posted_from.file_name(),
                "src_func", pending_task->posted_from.function_name());
 
   tracked_objects::TrackedTime start_time =
       tracked_objects::ThreadData::NowForStartOfRun(pending_task->birth_tally);
 
   g_worker_pool_running_on_this_thread.Get().Set(true);
   pending_task->task.Run();
   g_worker_pool_running_on_this_thread.Get().Set(false);
 
@@ skipping 29 matching lines @@
   PendingTask* pending_task = new PendingTask(from_here, task);
   return PostTaskInternal(pending_task, task_is_slow);
 }
 
 // static
 bool WorkerPool::RunsTasksOnCurrentThread() {
   return g_worker_pool_running_on_this_thread.Get().Get();
 }
 
 }  // namespace base