cc: Add image decode queue functionality to image manager.

cc/tiles/decoded_image_tracker.h

Index: cc/tiles/decoded_image_tracker.h
diff --git a/cc/tiles/decoded_image_tracker.h b/cc/tiles/decoded_image_tracker.h
new file mode 100644
index 0000000000000000000000000000000000000000..2d303ee5fe9efa94182e0099131236d2a8c846cd
--- /dev/null
+++ b/cc/tiles/decoded_image_tracker.h
@@ -0,0 +1,56 @@
+// 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_DECODED_IMAGE_TRACKER_H_
+#define CC_TILES_DECODED_IMAGE_TRACKER_H_
+
+#include <utility>
+#include <vector>
+
+#include "base/bind.h"
+#include "cc/base/cc_export.h"
+#include "cc/tiles/image_controller.h"
+
+class SkImage;
+
+namespace cc {
+
+// This class is the main interface for the rest of the system to request
+// decodes. It is responsible for keeping the decodes locked for a number of
+// frames, specified as |kNumFramesToLock| in the implementation file.
+//
+// Note that it is safe to replace ImageController's cache without doing
+// anything special with this class, since it retains only ids to the decode
+// requests. When defunct ids are then used to try and unlock the image, they
+// are silently ignored.
+class CC_EXPORT DecodedImageTracker {
+ public:
+  DecodedImageTracker();
+  ~DecodedImageTracker();
+
+  void QueueImageDecode(sk_sp<const SkImage> image,
+                        const base::Closure& callback);
+  void NotifyFrameFinished();
+
+ private:
+  friend class TileManager;
+  friend class DecodedImageTrackerTest;
+
+  void set_image_controller(ImageController* controller) {
+    image_controller_ = controller;
+  }
+
+  void ImageDecodeFinished(const base::Closure& callback,
+                           ImageController::ImageDecodeRequestId id);
+
+  ImageController* image_controller_ = nullptr;
+  std::vector<std::pair<ImageController::ImageDecodeRequestId, int>>
+      locked_images_;
+
+  DISALLOW_COPY_AND_ASSIGN(DecodedImageTracker);
+};
+
+}  // namespace cc
+
+#endif  // CC_TILES_DECODED_IMAGE_TRACKER_H_