Change PostTask to use Flow v2.

base/debug/task_annotator.cc

Index: base/debug/task_annotator.cc
diff --git a/base/debug/task_annotator.cc b/base/debug/task_annotator.cc
index b74d390938d75867af4f52d379774ae6fe265667..cfe5662301e1982df8606ac061b4a8751ea62ff8 100644
--- a/base/debug/task_annotator.cc
+++ b/base/debug/task_annotator.cc
@@ -20,9 +20,10 @@ TaskAnnotator::~TaskAnnotator() {
 
 void TaskAnnotator::DidQueueTask(const char* queue_function,
                                  const PendingTask& pending_task) {
-  TRACE_EVENT_FLOW_BEGIN0(TRACE_DISABLED_BY_DEFAULT("toplevel.flow"),
-                          queue_function,
-                          TRACE_ID_MANGLE(GetTaskTraceID(pending_task)));
+  TRACE_EVENT_WITH_FLOW0("toplevel",

[dsinclair, 2015/08/05 19:38:04]

The category should still be TRACE_DISABLED_BY_DEFAULT("toplevel.flow")

+                          "QueueTask",

[dsinclair, 2015/08/05 19:38:04]

Why did you change the name from queue_function?

[yuhaoz, 2015/08/05 21:22:07]

Because queue_function is the name of the original flow events. But with
TRACE_EVENT_WITH_FLOW, we are creating a slice, and the name here is going to be
the same of the slice. If we directly use queue_function, we will get the
following:


[               toplevel              ]                              [          
     toplevel         ]
     [MessageLoop::PostTask]   ------------------------------------------>  
[MessageLoop:PostTask]


This is because both the producer and consumer pass "MessageLoop:PostTask" as
queue_function.

The producer code:
https://code.google.com/p/chromium/codesearch#chromium/src/base/message_loop/...

The consumer code:
https://code.google.com/p/chromium/codesearch#chromium/src/base/message_loop/...

+                          TRACE_ID_MANGLE(GetTaskTraceID(pending_task)),
+                          TRACE_EVENT_FLAG_FLOW_OUT);
 }
 
 void TaskAnnotator::RunTask(const char* queue_function,
@@ -32,11 +33,14 @@ void TaskAnnotator::RunTask(const char* queue_function,
   tracked_objects::Duration queue_duration =
       stopwatch.StartTime() - pending_task.EffectiveTimePosted();
 
-  TRACE_EVENT_FLOW_END1(TRACE_DISABLED_BY_DEFAULT("toplevel.flow"),
-                        queue_function,
-                        TRACE_ID_MANGLE(GetTaskTraceID(pending_task)),
-                        "queue_duration",
-                        queue_duration.InMilliseconds());
+  {
+    TRACE_EVENT_WITH_FLOW1("toplevel",

[dsinclair, 2015/08/05 19:38:04]

TRACE_DISABLED_BY_DEFAULT("toplevel.flow")

+                            "RunTask",

[dsinclair, 2015/08/05 19:38:04]

Why did this change from queue_function to RunTask?

+                            TRACE_ID_MANGLE(GetTaskTraceID(pending_task)),
+                            TRACE_EVENT_FLAG_FLOW_IN,
+                            "queue_duration",
+                            queue_duration.InMilliseconds());
+  }
 
   // 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