CC: Add 'cc-benchmark' traces for minimal tracing in benchmarks.

base/message_loop/message_loop.cc

Index: base/message_loop/message_loop.cc
diff --git a/base/message_loop/message_loop.cc b/base/message_loop/message_loop.cc
index 8f6c9d8cb6f0d0901d1a6d7fdb1d04b871adc6a9..4e446df557e8c32fa1d2d70e7af50bbe4cbb9c02 100644
--- a/base/message_loop/message_loop.cc
+++ b/base/message_loop/message_loop.cc
@@ -412,17 +412,23 @@ bool MessageLoop::ProcessNextDelayedNonNestableTask() {
 }
 
 void MessageLoop::RunTask(const PendingTask& pending_task) {
+  // For absolutely minimal tracing, "toplevel" captures _everything_
+  // on a typical message loop thread, so long as the thread runs
+  // semi-regular tasks (for sufficient measurement granularity).

[epenner, 2014/02/12 02:02:16]

This is the primary tracing change. The rest just renames the other 'toplevel'
traces to be 'ipc' and 'task' again.

+  TRACE_EVENT_END0("toplevel", "All");
+  TRACE_EVENT_BEGIN0("toplevel", "All");
+
   tracked_objects::TrackedTime start_time =
       tracked_objects::ThreadData::NowForStartOfRun(pending_task.birth_tally);
 
-  TRACE_EVENT_FLOW_END1(TRACE_DISABLED_BY_DEFAULT("toplevel.flow"),
+  TRACE_EVENT_FLOW_END1(TRACE_DISABLED_BY_DEFAULT("task.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(
-      "toplevel", "MessageLoop::RunTask",
+      "task", "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());