content: Improve thread priority for raster threads.

content/renderer/raster_worker_pool.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 CONTENT_RENDERER_RASTER_WORKER_POOL_H_
 #define CONTENT_RENDERER_RASTER_WORKER_POOL_H_
 
 #include "base/callback.h"
 #include "base/containers/hash_tables.h"
 #include "base/macros.h"
@@ skipping 34 matching lines @@
   void WaitForTasksToFinishRunning(cc::NamespaceToken token) override;
   void CollectCompletedTasks(cc::NamespaceToken token,
                              cc::Task::Vector* completed_tasks) override;
 
   // Runs a task from one of the provided categories. Categories listed first
   // have higher priority.
   void Run(const std::vector<cc::TaskCategory>& categories);
 
   void FlushForTesting();
 
-  // Spawn |num_threads| number of threads and start running work on the
-  // worker threads.
-  void Start(int num_threads,
-             const base::SimpleThread::Options& thread_options);
+  // Spawn worker threads start running work on them. A seperate thread for
+  // background work is always created and |num_foreground_threads| the number
+  // of threads to use for foreground work.
+  void Start(int num_foreground_threads);
 
   // Finish running all the posted tasks (and nested task posted by those tasks)
   // of all the associated task runners.
   // Once all the tasks are executed the method blocks until the threads are
   // terminated.
   void Shutdown();
 
   cc::TaskGraphRunner* GetTaskGraphRunner() { return this; }
 
   // Create a new sequenced task graph runner.
@@ skipping 61 matching lines @@
   // Condition variable that is waited on by origin threads until a namespace
   // 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 content
 
 #endif  // CONTENT_RENDERER_RASTER_WORKER_POOL_H_