content: Implement dynamic priorities for raster threads.

cc/raster/synchronous_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_SYNCHRONOUS_TASK_GRAPH_RUNNER_H_
 #define CC_RASTER_SYNCHRONOUS_TASK_GRAPH_RUNNER_H_
 
 #include "cc/raster/task_graph_runner.h"
 #include "cc/raster/task_graph_work_queue.h"
 
 namespace cc {
 
 // Implements a TaskGraphRunner which runs synchronously. This runner only runs
 // tasks when RunUntilIdle is called.
-class CC_EXPORT SynchronousTaskGraphRunner : public TaskGraphRunner {
+class CC_EXPORT SynchronousTaskGraphRunner : public TaskGraphRunner,
+                                             public TaskGraphWorkQueueClient {
  public:
   SynchronousTaskGraphRunner();
   ~SynchronousTaskGraphRunner() 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 TaskGraphWorkQueueClient:
+  void AdjustWorkerPriorityForTask(Task* task,
+                                   uint16_t old_category,
+                                   uint16_t new_category) override {}
+
   // Runs all pending tasks from all namespaces.
   void RunUntilIdle();
 
  private:
   // Returns true if there was a task to run.
   bool RunTask();
 
   // Stores the actual tasks to be run, sorted by priority.
   TaskGraphWorkQueue work_queue_;
 };
 
 }  // namespace cc
 
 #endif  // CC_RASTER_SYNCHRONOUS_TASK_GRAPH_RUNNER_H_