cc: Reorder TileManager shutdown and add debugging information.

cc/tiles/image_manager.cc

 // Copyright 2016 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.
 
 #include "cc/tiles/image_manager.h"
 
 namespace cc {
 
 ImageManager::ImageManager() = default;
 ImageManager::~ImageManager() = default;
 
 void ImageManager::SetImageDecodeController(ImageDecodeController* controller) {
   // We can only switch from null to non-null and back.
-  DCHECK(controller || controller_);
-  DCHECK(!controller || !controller_);
+  // CHECK to debug crbug.com/650234.
+  CHECK(controller || controller_);
+  CHECK(!controller || !controller_);
 
   if (!controller) {
     SetPredecodeImages(std::vector<DrawImage>(),
                        ImageDecodeController::TracingInfo());
   }
   controller_ = controller;
+  // Debugging information for crbug.com/650234.
+  ++num_times_controller_was_set_;
 }
 
 void ImageManager::GetTasksForImagesAndRef(
     std::vector<DrawImage>* images,
     std::vector<scoped_refptr<TileTask>>* tasks,
     const ImageDecodeController::TracingInfo& tracing_info) {
   DCHECK(controller_);
   for (auto it = images->begin(); it != images->end();) {
     scoped_refptr<TileTask> task;
     bool need_to_unref_when_finished =
         controller_->GetTaskForImageAndRef(*it, tracing_info, &task);
     if (task)
       tasks->push_back(std::move(task));
 
     if (need_to_unref_when_finished)
       ++it;
     else
       it = images->erase(it);
   }
 }
 
 void ImageManager::UnrefImages(const std::vector<DrawImage>& images) {
-  DCHECK(controller_);
+  // Debugging information for crbug.com/650234.
+  CHECK(controller_) << num_times_controller_was_set_;
   for (auto image : images)
     controller_->UnrefImage(image);
 }
 
 void ImageManager::ReduceMemoryUsage() {
   DCHECK(controller_);
   controller_->ReduceCacheUsage();
 }
 
 std::vector<scoped_refptr<TileTask>> ImageManager::SetPredecodeImages(
     std::vector<DrawImage> images,
     const ImageDecodeController::TracingInfo& tracing_info) {
   std::vector<scoped_refptr<TileTask>> new_tasks;
   GetTasksForImagesAndRef(&images, &new_tasks, tracing_info);
   UnrefImages(predecode_locked_images_);
   predecode_locked_images_ = std::move(images);
   return new_tasks;
 }
 
 }  // namespace cc