cc: Fix RasterWorkerPool shutdown crash.

cc/raster_worker_pool.h

 // Copyright 2012 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_WORKER_POOL_H_
 #define CC_RASTER_WORKER_POOL_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 11 matching lines @@
 
 class RasterWorkerPool {
  public:
   explicit RasterWorkerPool(size_t num_raster_threads);
   virtual ~RasterWorkerPool();
 
   static scoped_ptr<RasterWorkerPool> Create(size_t num_raster_threads) {
     return make_scoped_ptr(new RasterWorkerPool(num_raster_threads));
   }
 
+  // Starts the worker pool. Returns true if the worker pool was successfully
+  // started; otherwise, returns false.
+  bool Start();
+
+  // Tells the worker pool to stop and returns once all pending tasks have
+  // completed.
+  void Stop();
+
+  // Returns true if the worker pool has been started, and not yet stopped.
+  bool IsRunning() const;
+
   bool IsBusy();
 
   void PostRasterTaskAndReply(PicturePileImpl* picture_pile,
                               uint8* buffer,
                               const gfx::Rect& rect,
                               float contents_scale,
                               const base::Closure& reply);
   void PostImageDecodeTaskAndReply(skia::LazyPixelRef* pixel_ref,
                                    const base::Closure& reply);
 
@@ skipping 40 matching lines @@
 
   Thread::Task* CreateTask();
   void DestroyTask(Thread::Task* task);
 
   void OnTaskCompleted(Thread::Task* task,
                        const base::Closure& reply);
   void OnRasterTaskCompleted(Thread::Task* task,
                              scoped_refptr<PicturePileImpl> picture_pile,
                              const base::Closure& reply);
 
+  void SortRasterThreadsIfNeeded();
+
+  bool is_running_;
+
   typedef std::vector<Thread*> ThreadVector;
   ThreadVector raster_threads_;
+  bool raster_threads_need_sorting_;
 
   DISALLOW_COPY_AND_ASSIGN(RasterWorkerPool);
 };
 
 }  // namespace cc
 
 #endif  // CC_RASTER_WORKER_POOL_H_