cc: Simplify task and its derived classes.

cc/test/task_graph_runner_test_template.cc

Index: cc/test/task_graph_runner_test_template.cc
diff --git a/cc/test/task_graph_runner_test_template.cc b/cc/test/task_graph_runner_test_template.cc
index 6797de2e665d0acca0a23fc6a8559bc96aafd367..67c1d21a12c29158d96a0c110639d76a89359028 100644
--- a/cc/test/task_graph_runner_test_template.cc
+++ b/cc/test/task_graph_runner_test_template.cc
@@ -22,13 +22,13 @@ void TaskGraphRunnerTestBase::RunAllTasks(int namespace_index) {
   task_graph_runner_->WaitForTasksToFinishRunning(
       namespace_token_[namespace_index]);
 
-  Task::Vector completed_tasks;
+  DependencyTask::Vector completed_tasks;
   task_graph_runner_->CollectCompletedTasks(namespace_token_[namespace_index],
                                             &completed_tasks);
-  for (Task::Vector::const_iterator it = completed_tasks.begin();
+  for (DependencyTask::Vector::const_iterator it = completed_tasks.begin();
        it != completed_tasks.end(); ++it) {
     FakeTaskImpl* task = static_cast<FakeTaskImpl*>(it->get());
-    task->CompleteOnOriginThread();
+    task->CompleteOnOriginThread(nullptr);
   }
 }
 
@@ -56,8 +56,8 @@ const std::vector<unsigned>& TaskGraphRunnerTestBase::on_task_completed_ids(
 void TaskGraphRunnerTestBase::ScheduleTasks(
     int namespace_index,
     const std::vector<TaskInfo>& tasks) {
-  Task::Vector new_tasks;
-  Task::Vector new_dependents;
+  DependencyTask::Vector new_tasks;
+  DependencyTask::Vector new_dependents;
   TaskGraph new_graph;
 
   for (std::vector<TaskInfo>::const_iterator it = tasks.begin();
@@ -92,7 +92,8 @@ void TaskGraphRunnerTestBase::FakeTaskImpl::RunOnWorkerThread() {
   test_->RunTaskOnWorkerThread(namespace_index_, id_);
 }
 
-void TaskGraphRunnerTestBase::FakeTaskImpl::CompleteOnOriginThread() {
+void TaskGraphRunnerTestBase::FakeTaskImpl::CompleteOnOriginThread(
+    DependencyTaskClient* client) {
   test_->OnTaskCompleted(namespace_index_, id_);
 }