cc: Rasterize cheap tiles immediately

cc/worker_pool.h

Index: cc/worker_pool.h
diff --git a/cc/worker_pool.h b/cc/worker_pool.h
index 26bce7aedd726c56ffa616a947d6986b67e34909..c7478f37435ddd20ffe7cc316196150d3d8d95e3 100644
--- a/cc/worker_pool.h
+++ b/cc/worker_pool.h
@@ -24,6 +24,7 @@ class WorkerPoolTask {
   virtual ~WorkerPoolTask();
 
   virtual void Run(RenderingStats* rendering_stats) = 0;
+  virtual void DeferToThread(base::Thread* thread) = 0;
 
   bool HasCompleted();
   void DidComplete();
@@ -121,6 +122,8 @@ class WorkerPool {
   WorkerPool(WorkerPoolClient* client, size_t num_threads);
 
   WorkerPool::Worker* GetWorkerForNextTask();
+  bool CanPostCheapTask() const;
+  void PostCheapTask(scoped_ptr<internal::WorkerPoolTask> task);
 
  private:
   class NumPendingTasksComparator {
@@ -151,6 +154,9 @@ class WorkerPool {
   // Ensure workers are sorted by number of pending tasks.
   void SortWorkersIfNeeded();
 
+  // Run pending cheap tasks on origin thread.
+  void RunCheapTasks();
+
   typedef std::vector<Worker*> WorkerVector;
   WorkerVector workers_;
   WorkerPoolClient* client_;
@@ -161,9 +167,15 @@ class WorkerPool {
   base::CancelableClosure check_for_completed_tasks_callback_;
   bool check_for_completed_tasks_pending_;
   base::Closure idle_callback_;
+  base::Closure cheap_task_callback_;
   // Accessed from multiple threads. 0 when worker pool is idle.
   base::subtle::Atomic32 pending_task_count_;
 
+  bool cheap_tasks_allowed_;
+  bool run_cheap_tasks_pending_;
+  ScopedPtrDeque<internal::WorkerPoolTask> pending_cheap_tasks_;
+  scoped_ptr<RenderingStats> cheap_rendering_stats_;
+
   DISALLOW_COPY_AND_ASSIGN(WorkerPool);
 };