cc: Simplify task and its derived classes.

cc/raster/bitmap_tile_task_worker_pool.cc

Index: cc/raster/bitmap_tile_task_worker_pool.cc
diff --git a/cc/raster/bitmap_tile_task_worker_pool.cc b/cc/raster/bitmap_tile_task_worker_pool.cc
index 783ec4841951078b89c80abe1d36866f893e74ff..4c0b644c5fe54f88966db582bc6f9acddd057155 100644
--- a/cc/raster/bitmap_tile_task_worker_pool.cc
+++ b/cc/raster/bitmap_tile_task_worker_pool.cc
@@ -15,7 +15,6 @@
 #include "base/trace_event/trace_event_argument.h"
 #include "cc/debug/traced_value.h"
 #include "cc/playback/raster_source.h"
-#include "cc/raster/raster_buffer.h"
 #include "cc/resources/platform_color.h"
 #include "cc/resources/resource.h"
 
@@ -102,7 +101,7 @@ void BitmapTileTaskWorkerPool::Shutdown() {
 void BitmapTileTaskWorkerPool::ScheduleTasks(TaskGraph* graph) {
   TRACE_EVENT0("cc", "BitmapTileTaskWorkerPool::ScheduleTasks");
 
-  ScheduleTasksOnOriginThread(this, graph);
+  ScheduleTasksOnOriginThread(graph);
   task_graph_runner_->ScheduleTasks(namespace_token_, graph);
 }
 
@@ -113,10 +112,10 @@ void BitmapTileTaskWorkerPool::CheckForCompletedTasks() {
                                             &completed_tasks_);
   for (Task::Vector::const_iterator it = completed_tasks_.begin();
        it != completed_tasks_.end(); ++it) {
-    TileTask* task = static_cast<TileTask*>(it->get());
+    Task* task = it->get();
 
     task->WillComplete();
-    task->CompleteOnOriginThread(this);
+    task->CompleteOnOriginThread();
     task->DidComplete();
   }
   completed_tasks_.clear();