cc: Add ImageManager to keep all the image locking in the same place.

cc/tiles/image_manager.h

+// 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.
+
+#ifndef CC_TILES_IMAGE_MANAGER_H_
+#define CC_TILES_IMAGE_MANAGER_H_
+
+#include <vector>
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "cc/base/cc_export.h"
+#include "cc/playback/draw_image.h"
+#include "cc/raster/tile_task.h"
+#include "cc/tiles/image_decode_controller.h"
+
+namespace cc {
+
+class CC_EXPORT ImageManager {

[enne (OOO), 2016/09/15 17:42:15]

What else do you see going into this class? I think this patch seems fine on its
own, but because I'm not sure I see what else is moving in here it's hard to
tell.

[vmpstr, 2016/09/15 18:16:35]

The next thing I was thinking is "SetPredecodeImages" which takes a set of
images and returns a set of tasks. This eliminates 2 members from tile manager.
This would also handle unreffing old images, eliminating that code from TM. 

Later, I was thinking this would be the class keeping track of which images are
checkered, providing tasks for it, and providing invalidation signals for when
the images are decoded.

+ public:
+  ImageManager();
+  ~ImageManager();
+
+  void SetImageDecodeController(ImageDecodeController* controller);
+  void GetTasksForImagesAndRef(
+      std::vector<DrawImage>* images,
+      std::vector<scoped_refptr<TileTask>>* tasks,
+      const ImageDecodeController::TracingInfo& tracing_info);
+  void UnrefImages(const std::vector<DrawImage>& images);
+  void ReduceMemoryUsage();
+
+ private:
+  ImageDecodeController* controller_;
+
+  DISALLOW_COPY_AND_ASSIGN(ImageManager);
+};
+
+}  // namespace cc
+
+#endif  // CC_TILES_IMAGE_MANAGER_H_