cc: Simplify task and its derived classes.

cc/raster/gpu_tile_task_worker_pool.cc

Index: cc/raster/gpu_tile_task_worker_pool.cc
diff --git a/cc/raster/gpu_tile_task_worker_pool.cc b/cc/raster/gpu_tile_task_worker_pool.cc
index e54672e6f1aebb3492ad2e3ee33409350acac592..4c8d9c7be8e1c9e3a66c279aaec194ad90dd5384 100644
--- a/cc/raster/gpu_tile_task_worker_pool.cc
+++ b/cc/raster/gpu_tile_task_worker_pool.cc
@@ -166,13 +166,11 @@ bool GpuTileTaskWorkerPool::GetResourceRequiresSwizzle(
   return false;
 }
 
-void GpuTileTaskWorkerPool::CompleteTasks(const Task::Vector& tasks) {
+void GpuTileTaskWorkerPool::CompleteTasks(const DependencyTask::Vector& tasks) {
   for (auto& task : tasks) {
-    TileTask* tile_task = static_cast<TileTask*>(task.get());
-
-    tile_task->WillComplete();
-    tile_task->CompleteOnOriginThread(this);
-    tile_task->DidComplete();
+    task->WillComplete();
+    task->CompleteOnOriginThread(this);
+    task->DidComplete();
   }
   completed_tasks_.clear();
 }