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

third_party/WebKit/public/platform/WebThread.h

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 38 matching lines @@
         virtual void run(double deadlineSeconds) = 0;
     };
 
     class BLINK_PLATFORM_EXPORT TaskObserver {
     public:
         virtual ~TaskObserver() { }
         virtual void willProcessTask() = 0;
         virtual void didProcessTask() = 0;
     };
 
+    class BLINK_PLATFORM_EXPORT TaskTimeObserver {
+    public:
+        virtual ~TaskTimeObserver() { }
+        virtual void willProcessTask() = 0;

[Sami, 2016/08/19 14:44:56]

Could you remind me why we need did/willProcess again? In any case they're
redundant with TaskObserver so should probably just reuse that.

[panicker, 2016/08/19 18:06:50]

This is to line up the Begin / End with Time Reporting exactly.
For instance, I think I will get additional willProcess / DidProcess without
corresponding reportTaskTime -- because of the !delegate check in
task_queue_manager (the condition is present for reportTaskTime but not for the
willProcess / DidProcess)

[panicker, 2016/08/19 18:10:53]

If you can suggest a completely different way to hook up WebPerfAgent to the
scheduler (i.e. not involving WebThread) that might work too. Thoughts?

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

The task observer can also check if it is nested. Basically you'll get another
willProcess() call before the corresponding didProcess().

+        virtual void didProcessTask() = 0;
+        virtual void reportTaskTime(double, double) = 0;
+    };
 
     // Returns a WebTaskRunner bound to the underlying scheduler's default task queue.
     virtual WebTaskRunner* getWebTaskRunner() { return nullptr; }
 
     virtual bool isCurrentThread() const = 0;
     virtual PlatformThreadId threadId() const { return 0; }
 
     virtual void addTaskObserver(TaskObserver*) { }
     virtual void removeTaskObserver(TaskObserver*) { }
+    virtual void addTaskTimeObserver(TaskTimeObserver*) { }
+    virtual void removeTaskTimeObserver(TaskTimeObserver*) { }
 
     // Returns the scheduler associated with the thread.
     virtual WebScheduler* scheduler() const = 0;
 
     virtual ~WebThread() { }
 };
 
 } // namespace blink
 
 #endif