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

base/message_loop/incoming_task_queue.cc

 // Copyright 2013 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/message_loop/incoming_task_queue.h"
 
 #include "base/debug/trace_event.h"
 #include "base/location.h"
 #include "base/message_loop/message_loop.h"
 #include "base/synchronization/waitable_event.h"
@@ skipping 112 matching lines @@
   if (!message_loop_) {
     pending_task->task.Reset();
     return false;
   }
 
   // Initialize the sequence number. The sequence number is used for delayed
   // tasks (to faciliate FIFO sorting when two tasks have the same
   // delayed_run_time value) and for identifying the task in about:tracing.
   pending_task->sequence_num = next_sequence_num_++;
 
-  TRACE_EVENT_FLOW_BEGIN0("task", "MessageLoop::PostTask",
+  TRACE_EVENT_FLOW_BEGIN0(TRACE_DISABLED_BY_DEFAULT("toplevel.flow"),
+      "MessageLoop::PostTask",
       TRACE_ID_MANGLE(message_loop_->GetTaskTraceID(*pending_task)));
 
   bool was_empty = incoming_queue_.empty();
   incoming_queue_.push(*pending_task);
   pending_task->task.Reset();
 
   // Wake up the pump.
   message_loop_->ScheduleWork(was_empty);
 
   return true;
 }
 
 }  // namespace internal
 }  // namespace base