Adds the concept of Policies to the Blink Scheduler

Source/platform/scheduler/Scheduler.h

Index: Source/platform/scheduler/Scheduler.h
diff --git a/Source/platform/scheduler/Scheduler.h b/Source/platform/scheduler/Scheduler.h
index 9524ec37a34d76596985ea4f2c438e84bb52dbef..11676e904fbc6fde6c6f7423c522bf7bb8fefbc1 100644
--- a/Source/platform/scheduler/Scheduler.h
+++ b/Source/platform/scheduler/Scheduler.h
@@ -54,12 +54,17 @@ public:
     void setSharedTimerFireInterval(double);
     void stopSharedTimer();
 
-private:
+protected:
     class MainThreadPendingTaskRunner;
     class MainThreadPendingHighPriorityTaskRunner;
     friend class MainThreadPendingTaskRunner;
     friend class MainThreadPendingHighPriorityTaskRunner;
 
+    enum SchedulerPolicy {
+        Normal,
+        CompositorPriority,
+    };
+
     class TracedTask {
     public:
         TracedTask(const Task& task, const TraceLocation& location)
@@ -74,29 +79,47 @@ private:
     };
 
     Scheduler();
-    ~Scheduler();
-
-    void scheduleIdleTask(const TraceLocation&, const IdleTask&);
+    virtual ~Scheduler();
 
     static void sharedTimerAdapter();
-    void tickSharedTimer();
 
-    bool hasPendingHighPriorityWork() const;
+
+    // Start of main thread only members -----------------------------------
+
+    // Only does work in CompositorPriority mode. Returns true if any work was done.
+    bool runPendingHighPriorityTasksIfInCompositorPriority();
+
+    // Returns true if any work was done.
     bool swapQueuesAndRunPendingTasks();
+
     void swapQueuesRunPendingTasksAndAllowHighPriorityTaskRunnerPosting();
 
     // Returns true if any work was done.
     bool executeHighPriorityTasks(Deque<TracedTask>&);
 
+    // Return the current SchedulerPolicy.
+    SchedulerPolicy schedulerPolicy() const;
+
+    void maybeEnterNormalschedulerPolicy();

[Sami, 2014/09/11 11:32:18]

Please capitalize "scheduler" here.

+
     // Must be called while m_pendingTasksMutex is locked.
     void maybePostMainThreadPendingHighPriorityTaskRunner();
 
-    static Scheduler* s_sharedScheduler;
+    void tickSharedTimer();
 
-    // Should only be accessed from the main thread.
     void (*m_sharedTimerFunction)();
 
-    // These members can be accessed from any thread.
+    // End of main thread only members -------------------------------------
+
+
+    void scheduleIdleTask(const TraceLocation&, const IdleTask&);
+
+    bool hasPendingHighPriorityWork() const;
+
+    void enterSchedulerPolicy(SchedulerPolicy);
+
+    static Scheduler* s_sharedScheduler;
+
     WebThread* m_mainThread;
 
     // This mutex protects calls to the pending task queue and m_highPriorityTaskRunnerPosted.
@@ -105,6 +128,10 @@ private:
 
     volatile int m_highPriorityTaskCount;
     bool m_highPriorityTaskRunnerPosted;
+
+    // Don't access m_schedulerPolicy directly, use enterSchedulerPolicy and SchedulerPolicy instead.
+    volatile int m_schedulerPolicy;
+    double m_compositorPriorityPolicyEndTimeSeconds;

[Sami, 2014/09/11 11:32:18]

This is protected by m_pendingTasksMutex, right? Could you move it over to that
section?

 };
 
 } // namespace blink