Add support for calculating the position of the top controls in the cc layer.

cc/top_controls_manager.h

Index: cc/top_controls_manager.h
diff --git a/cc/top_controls_manager.h b/cc/top_controls_manager.h
new file mode 100644
index 0000000000000000000000000000000000000000..5ca77187e4253fead0b45df07697b23b6a6723b1
--- /dev/null
+++ b/cc/top_controls_manager.h
@@ -0,0 +1,74 @@
+// 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_TOP_CONTROLS_MANAGER_H_
+#define CC_TOP_CONTROLS_MANAGER_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "base/timer.h"
+#include "cc/layer_impl.h"
+#include "ui/gfx/size.h"
+#include "ui/gfx/vector2d_f.h"
+
+namespace base {
+class TimeTicks;
+}
+
+namespace cc {
+
+class LayerTreeImpl;
+class TopControlsAnimation;
+class TopControlsManagerClient;
+
+// Manages the position of the top controls.
+class TopControlsManager {
+ public:
+  static scoped_ptr<TopControlsManager> Create(TopControlsManagerClient* client,
+                                               float top_controls_height);
+  virtual ~TopControlsManager();
+
+  float controls_top_offset() { return controls_top_offset_; }
+  float content_top_offset() { return content_top_offset_; }
+  float is_overlay_mode() { return is_overlay_mode_; }
+  TopControlsAnimation* animation() { return top_controls_animation_.get(); }
+
+  void UpdateDrawPositions();
+
+  void ScrollBegin();
+  gfx::Vector2dF ScrollBy(const gfx::Vector2dF pending_delta);
+  void ScrollEnd();
+
+  void Animate(base::TimeTicks monotonic_time);
+
+ protected:
+  TopControlsManager(TopControlsManagerClient* client,
+                     float top_controls_height);
+
+ private:
+  gfx::Vector2dF ScrollInternal(const gfx::Vector2dF pending_delta);
+  void ResetAnimations();
+  LayerImpl* RootScrollLayer();
+  float RootScrollLayerTotalScrollY();
+  void StartAnimationIfNecessary();
+  void StartAutoHideAnimation();
+
+  TopControlsManagerClient* client_;  // The client manages the lifecycle of
+                                      // this.
+
+  base::OneShotTimer<TopControlsManager> auto_hide_timer_;
+  scoped_ptr<TopControlsAnimation> top_controls_animation_;
+  bool is_overlay_mode_;
+  float controls_top_offset_;
+  float content_top_offset_;
+  float top_controls_height_;
+  bool scroll_readjustment_enabled_;
+  float previous_root_scroll_offset_;
+
+  DISALLOW_COPY_AND_ASSIGN(TopControlsManager);
+};
+
+}  // namespace cc
+
+#endif  // CC_TOP_CONTROLS_MANAGER_H_