Move and rename TaskTimeTracker to public interface exposed to WebThread, use in WebPerf Agent.

third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.h

Index: third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.h
diff --git a/third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.h b/third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.h
index 7e84e40b8ce5d69bdb2427ac808e5c71d67ed890..cd4b8d7366a3ff33751add191f9d0d3ab731a1cb 100644
--- a/third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.h
+++ b/third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.h
@@ -18,6 +18,7 @@
 #include "platform/scheduler/base/enqueue_order.h"
 #include "platform/scheduler/base/task_queue_impl.h"
 #include "platform/scheduler/base/task_queue_selector.h"
+#include "public/platform/WebThread.h"
 
 namespace base {
 class TickClock;
@@ -38,7 +39,6 @@ class LazyNow;
 class RealTimeDomain;
 class TimeDomain;
 class TaskQueueManagerDelegate;
-class TaskTimeTracker;
 
 // The task queue manager provides N task queues and a selector interface for
 // choosing which task queue to service next. Each task queue consists of two
@@ -83,17 +83,12 @@ class BLINK_PLATFORM_EXPORT TaskQueueManager
   // tasks posted to the main loop. The batch size is 1 by default.
   void SetWorkBatchSize(int work_batch_size);
 
-  // When given a non-null TaskTimeTracker, the TaskQueueManager calls its
-  // ReportTaskTime method for every top level task. The task_time_tracker must
-  // outlive this object, or be removed via SetTaskTimeTracker(nullptr).
-  void SetTaskTimeTracker(TaskTimeTracker* task_time_tracker) {
-    task_time_tracker_ = task_time_tracker;
-  }
-
   // These functions can only be called on the same thread that the task queue
   // manager executes its tasks on.
   void AddTaskObserver(base::MessageLoop::TaskObserver* task_observer);
   void RemoveTaskObserver(base::MessageLoop::TaskObserver* task_observer);
+  void AddTaskTimeObserver(WebThread::TaskTimeObserver* task_time_observer);

[Sami, 2016/08/22 15:51:30]

Earlier I really should've talked about base/ vs. not-base since as you rightly
pointed out, WebThread is in platform/ too. Anyway, what I was trying to say was
that scheduler/base is used to implement WebThread, so it's a little odd for it
to depend on it too. How about instead we do this:

1. Add an abstract TaskTimeObserver class here (a separate header maybe).
2. Add a "using scheduler::TaskTimeObserver" in WebThread to bring it into scope
(or we could just use it directly there).

WDYT?

[panickercorp, 2016/08/22 16:55:45]

I agree it makes sense to make it a separate interface and decouple from
WebThread, given what you said.
However the question is whether it should live in:
third_party/WebKit/public/platform/  OR
third_party/WebKit/public/platform/scheduler/base/
The former seems like it would be more consistent with existing code structure
and deps than latter.
However I'll start with latter and see what folks think.

[Sami, 2016/08/22 17:02:58]

The latter sounds good to me. I think we're still figuring out how the scheduler
code will eventually meld into Blink.

[panicker, 2016/08/22 23:14:14]

Done.

+  void RemoveTaskTimeObserver(WebThread::TaskTimeObserver* task_time_observer);
 
   // Returns true if any task from a monitored task queue was was run since the
   // last call to GetAndClearSystemIsQuiescentBit.
@@ -248,7 +243,8 @@ class BLINK_PLATFORM_EXPORT TaskQueueManager
 
   base::ObserverList<base::MessageLoop::TaskObserver> task_observers_;
 
-  TaskTimeTracker* task_time_tracker_;  // NOT OWNED
+  bool has_task_time_observer;

[alph, 2016/08/22 22:21:27]

Is it used?

[panicker, 2016/08/22 23:14:14]

Removed in new patch

+  base::ObserverList<WebThread::TaskTimeObserver> task_time_observers_;
 
   const char* tracing_category_;
   const char* disabled_by_default_tracing_category_;