cc: Reuse the same TaskGraph and completed tasks vector.

cc/resources/image_raster_worker_pool.h

Index: cc/resources/image_raster_worker_pool.h
diff --git a/cc/resources/image_raster_worker_pool.h b/cc/resources/image_raster_worker_pool.h
index a349564ad62fb4977df8c0311e44ca5c069697e2..d2dabbb07f938e61c143848ce0d1e3ba44d09ccd 100644
--- a/cc/resources/image_raster_worker_pool.h
+++ b/cc/resources/image_raster_worker_pool.h
@@ -50,6 +50,11 @@ class CC_EXPORT ImageRasterWorkerPool : public RasterWorkerPool {
   bool raster_tasks_pending_;
   bool raster_tasks_required_for_activation_pending_;
 
+  // Task graph used when scheduling tasks and vector used to gather
+  // completed tasks.
+  internal::TaskGraph graph_;
+  internal::Task::Vector completed_tasks_;
+
   DISALLOW_COPY_AND_ASSIGN(ImageRasterWorkerPool);
 };