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

third_party/WebKit/public/platform/WebThread.h

Index: third_party/WebKit/public/platform/WebThread.h
diff --git a/third_party/WebKit/public/platform/WebThread.h b/third_party/WebKit/public/platform/WebThread.h
index c9a45b6f57ed9ab753eaf8769be1054f4526a3ff..2ef0627496000bb7e1e6abae6664af8410ca71f2 100644
--- a/third_party/WebKit/public/platform/WebThread.h
+++ b/third_party/WebKit/public/platform/WebThread.h
@@ -26,6 +26,8 @@
 #define WebThread_h
 
 #include "WebCommon.h"
+#include "public/platform/scheduler/base/task_time_tracker.h"

[Sami, 2016/08/23 10:34:59]

nit: Could forward declare this instead.

[panickercorp, 2016/08/23 17:43:31]

Done.

+
 #include <stdint.h>
 
 namespace blink {
@@ -66,6 +68,9 @@ public:
     virtual void addTaskObserver(TaskObserver*) { }

[Sami, 2016/08/23 10:34:59]

Could you add a comment here saying that both the task observer and task time
tracker APIs are very sensitive to performance and must not be used without a
good reason?

[panickercorp, 2016/08/23 17:43:31]

How is this?

     virtual void removeTaskObserver(TaskObserver*) { }
 
+    virtual void addTaskTimeTracker(scheduler::TaskTimeTracker*) {}
+    virtual void removeTaskTimeTracker(scheduler::TaskTimeTracker*) {}
+
     // Returns the scheduler associated with the thread.
     virtual WebScheduler* scheduler() const = 0;