cc: Move (partially) the predecode image tracking to ImageManager.

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_);
+
+  if (!controller) {
+    SetPredecodeImages(std::vector<DrawImage>(),
+                       ImageDecodeController::TracingInfo());
+  }
   controller_ = controller;
 }
 
 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;
@@ skipping 13 matching lines @@
   DCHECK(controller_);
   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