cc: Simplify raster task completion notification logic

cc/resources/pixel_buffer_raster_worker_pool.h

Index: cc/resources/pixel_buffer_raster_worker_pool.h
diff --git a/cc/resources/pixel_buffer_raster_worker_pool.h b/cc/resources/pixel_buffer_raster_worker_pool.h
index 88be2c02a7f8901cc5899eefefe8bd65256bf463..5fd0a002b0e2ffdbc1f96289aa581fa199528a75 100644
--- a/cc/resources/pixel_buffer_raster_worker_pool.h
+++ b/cc/resources/pixel_buffer_raster_worker_pool.h
@@ -44,10 +44,16 @@ class CC_EXPORT PixelBufferRasterWorkerPool : public RasterWorkerPool {
                               size_t num_threads,
                               size_t max_transfer_buffer_usage_bytes);
 
+  enum TaskQueueCompletionStatus {
+    TASKS_PENDING,
+    TASKS_REQUIRED_FOR_ACTIVATION_COMPLETED,
+    ALL_TASKS_COMPLETED
+  };
+
   void FlushUploads();
   void CheckForCompletedUploads();
   void ScheduleCheckForCompletedRasterTasks();
-  void CheckForCompletedRasterTasks();
+  TaskQueueCompletionStatus CheckForCompletedRasterTasks();
   void ScheduleMoreTasks();
   void OnRasterTaskCompleted(
       scoped_refptr<internal::RasterWorkerPoolTask> task,