cc: Simplify task and its derived classes.

cc/raster/task_graph_work_queue.h

Index: cc/raster/task_graph_work_queue.h
diff --git a/cc/raster/task_graph_work_queue.h b/cc/raster/task_graph_work_queue.h
index 0c82f67678a73be42e3424c6c27170ddcc716260..8833b6907482970a801ac29dc420ee64cc759488 100644
--- a/cc/raster/task_graph_work_queue.h
+++ b/cc/raster/task_graph_work_queue.h
@@ -31,7 +31,7 @@ class CC_EXPORT TaskGraphWorkQueue {
   struct PrioritizedTask {
     typedef std::vector<PrioritizedTask> Vector;
 
-    PrioritizedTask(Task* task,
+    PrioritizedTask(DependencyTask* task,
                     TaskNamespace* task_namespace,
                     uint16_t category,
                     uint16_t priority)
@@ -40,13 +40,13 @@ class CC_EXPORT TaskGraphWorkQueue {
           category(category),
           priority(priority) {}
 
-    Task* task;
+    DependencyTask* task;
     TaskNamespace* task_namespace;
     uint16_t category;
     uint16_t priority;
   };
 
-  using CategorizedTask = std::pair<uint16_t, scoped_refptr<Task>>;
+  using CategorizedTask = std::pair<uint16_t, scoped_refptr<DependencyTask>>;
 
   // Helper classes and static methods used by dependent classes.
   struct TaskNamespace {
@@ -64,7 +64,7 @@ class CC_EXPORT TaskGraphWorkQueue {
     std::map<uint16_t, PrioritizedTask::Vector> ready_to_run_tasks;
 
     // Completed tasks not yet collected by origin thread.
-    Task::Vector completed_tasks;
+    DependencyTask::Vector completed_tasks;
 
     // This set contains all currently running tasks.
     std::vector<CategorizedTask> running_tasks;
@@ -91,7 +91,7 @@ class CC_EXPORT TaskGraphWorkQueue {
   // Helper which populates a vector of completed tasks from the provided
   // namespace.
   void CollectCompletedTasks(NamespaceToken token,
-                             Task::Vector* completed_tasks);
+                             DependencyTask::Vector* completed_tasks);
 
   // Helper which returns the raw TaskNamespace* for the given token. Used to
   // allow callers to re-use a TaskNamespace*, reducing the number of lookups