cc: Simplify task and its derived classes.

cc/raster/synchronous_task_graph_runner.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/raster/synchronous_task_graph_runner.h"
 
 #include <stdint.h>
 
 #include <algorithm>
 #include <utility>
@@ skipping 36 matching lines @@
     return;
 
   while (!work_queue_.HasFinishedRunningTasksInNamespace(task_namespace)) {
     bool succeeded = RunTask();
     DCHECK(succeeded);
   }
 }
 
 void SynchronousTaskGraphRunner::CollectCompletedTasks(
     NamespaceToken token,
-    Task::Vector* completed_tasks) {
+    DependencyTask::Vector* completed_tasks) {
   TRACE_EVENT0("cc", "SynchronousTaskGraphRunner::CollectCompletedTasks");
 
   DCHECK(token.IsValid());
   work_queue_.CollectCompletedTasks(token, completed_tasks);
 }
 
 void SynchronousTaskGraphRunner::RunUntilIdle() {
   while (RunTask()) {
   }
 }
 
 bool SynchronousTaskGraphRunner::RunTask() {
   TRACE_EVENT0("toplevel", "SynchronousTaskGraphRunner::RunTask");
 
   // Find the first category with any tasks to run. This task graph runner
   // treats categories as an additional priority.
   const auto& ready_to_run_namespaces = work_queue_.ready_to_run_namespaces();
   auto found = std::find_if(
       ready_to_run_namespaces.cbegin(), ready_to_run_namespaces.cend(),
       [](const std::pair<uint16_t, TaskGraphWorkQueue::TaskNamespace::Vector>&
              pair) { return !pair.second.empty(); });
 
   if (found == ready_to_run_namespaces.cend()) {
     return false;
   }
 
   const uint16_t category = found->first;
   auto prioritized_task = work_queue_.GetNextTaskToRun(category);
 
-  Task* task = prioritized_task.task;
+  DependencyTask* task = prioritized_task.task;
   task->WillRun();
   task->RunOnWorkerThread();
   task->DidRun();
 
   work_queue_.CompleteTask(prioritized_task);
 
   return true;
 }
 
 }  // namespace cc