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

base/message_loop/message_loop.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/message_loop.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
@@ skipping 398 matching lines @@
   deferred_non_nestable_work_queue_.pop();
 
   RunTask(pending_task);
   return true;
 }
 
 void MessageLoop::RunTask(const PendingTask& pending_task) {
   tracked_objects::TrackedTime start_time =
       tracked_objects::ThreadData::NowForStartOfRun(pending_task.birth_tally);
 
-  TRACE_EVENT_FLOW_END1("task", "MessageLoop::PostTask",
-      TRACE_ID_MANGLE(GetTaskTraceID(pending_task)),
+  TRACE_EVENT_FLOW_END1(TRACE_DISABLED_BY_DEFAULT("toplevel.flow"),
+      "MessageLoop::PostTask", TRACE_ID_MANGLE(GetTaskTraceID(pending_task)),
       "queue_duration",
       (start_time - pending_task.EffectiveTimePosted()).InMilliseconds());
   // When tracing memory for posted tasks it's more valuable to attribute the
   // memory allocations to the source function than generically to "RunTask".
   TRACE_EVENT_WITH_MEMORY_TAG2(
-      "task", "MessageLoop::RunTask",
+      "toplevel", "MessageLoop::RunTask",
       pending_task.posted_from.function_name(),  // Name for memory tracking.
       "src_file", pending_task.posted_from.file_name(),
       "src_func", pending_task.posted_from.function_name());
 
   DCHECK(nestable_tasks_allowed_);
   // Execute the task and assume the worst: It is probably not reentrant.
   nestable_tasks_allowed_ = false;
 
   // Before running the task, store the program counter where it was posted
   // and deliberately alias it to ensure it is on the stack if the task
@@ skipping 282 matching lines @@
       fd,
       persistent,
       mode,
       controller,
       delegate);
 }
 
 #endif
 
 }  // namespace base