content: Implement dynamic priorities for raster threads.

cc/raster/single_thread_task_graph_runner.h

 // 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.
 
 #ifndef CC_RASTER_SINGLE_THREAD_TASK_GRAPH_RUNNER_H_
 #define CC_RASTER_SINGLE_THREAD_TASK_GRAPH_RUNNER_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "base/synchronization/condition_variable.h"
 #include "base/threading/simple_thread.h"
 #include "cc/raster/task_graph_runner.h"
 #include "cc/raster/task_graph_work_queue.h"
 
 namespace base {
 class SimpleThread;
 }
 
 namespace cc {
 
 // Runs TaskGraphs asynchronously using a single worker thread.
 class CC_EXPORT SingleThreadTaskGraphRunner
     : public TaskGraphRunner,
-      public base::DelegateSimpleThread::Delegate {
+      public base::DelegateSimpleThread::Delegate,
+      public TaskGraphWorkQueueClient {
  public:
   SingleThreadTaskGraphRunner();
   ~SingleThreadTaskGraphRunner() override;
 
   // Overridden from TaskGraphRunner:
   NamespaceToken GetNamespaceToken() override;
   void ScheduleTasks(NamespaceToken token, TaskGraph* graph) override;
   void WaitForTasksToFinishRunning(NamespaceToken token) override;
   void CollectCompletedTasks(NamespaceToken token,
                              Task::Vector* completed_tasks) override;
 
   // Overridden from base::DelegateSimpleThread::Delegate:
   void Run() override;
 
+  // Overridden from TaskGraphWorkQueueClient:
+  void AdjustWorkerPriorityForTask(Task* task,
+                                   uint16_t old_category,
+                                   uint16_t new_category) override {}
+
   void Start(const std::string& thread_name,
              const base::SimpleThread::Options& thread_options);
   void Shutdown();
 
  private:
   // Returns true if there was a task to run.
   bool RunTaskWithLockAcquired();
 
   scoped_ptr<base::SimpleThread> thread_;
 
@@ skipping 12 matching lines @@
   // has finished running all associated tasks.
   base::ConditionVariable has_namespaces_with_finished_running_tasks_cv_;
 
   // Set during shutdown. Tells Run() to return when no more tasks are pending.
   bool shutdown_;
 };
 
 }  // namespace cc
 
 #endif  // CC_RASTER_SINGLE_THREAD_TASK_GRAPH_RUNNER_H_