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 27d0a4651559e8a5d2402a09aaa422e9824924ca..3142fb77abc4b371f0f0ad2fe97b4c2ead43911a 100644
--- a/cc/raster/gpu_tile_task_worker_pool.cc
+++ b/cc/raster/gpu_tile_task_worker_pool.cc
@@ -12,7 +12,6 @@
 #include "base/trace_event/trace_event.h"
 #include "cc/playback/raster_source.h"
 #include "cc/raster/gpu_rasterizer.h"
-#include "cc/raster/raster_buffer.h"
 #include "cc/raster/scoped_gpu_raster.h"
 #include "cc/resources/resource.h"
 #include "gpu/command_buffer/client/gles2_interface.h"
@@ -135,7 +134,7 @@ void GpuTileTaskWorkerPool::Shutdown() {
 void GpuTileTaskWorkerPool::ScheduleTasks(TaskGraph* graph) {
   TRACE_EVENT0("cc", "GpuTileTaskWorkerPool::ScheduleTasks");
 
-  ScheduleTasksOnOriginThread(this, graph);
+  ScheduleTasksOnOriginThread(graph);
 
   // Barrier to sync any new resources to the worker context.
   rasterizer_->resource_provider()
@@ -167,13 +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();
+    task->DidComplete();
   }
   completed_tasks_.clear();
 }