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

third_party/WebKit/public/platform/WebThread.h

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 #ifndef WebThread_h
 #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 {
 class WebScheduler;
 class WebTaskRunner;
 
 // Always an integer value.
 typedef uintptr_t PlatformThreadId;
 
 // Provides an interface to an embedder-defined thread implementation.
@@ skipping 17 matching lines @@
         virtual void didProcessTask() = 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*) { }

[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;
 
     virtual ~WebThread() { }
 };
 
 } // namespace blink
 
 #endif