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

cc/top_controls_animation.h

Index: cc/top_controls_animation.h
diff --git a/cc/top_controls_animation.h b/cc/top_controls_animation.h
new file mode 100644
index 0000000000000000000000000000000000000000..dc9c122de01139e6d06897628b6ee7abe9dbaafe
--- /dev/null
+++ b/cc/top_controls_animation.h
@@ -0,0 +1,56 @@
+// 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_ANIMATION_H_
+#define CC_TOP_CONTROLS_ANIMATION_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "base/time.h"
+#include "ui/gfx/size.h"
+#include "ui/gfx/vector2d_f.h"
+
+namespace cc {
+
+class TimingFunction;
+
+// A small helper class that does the math for animations pertaining to the
+// position of the top controls.
+//
+// All sizes and vectors in this class's public methods are in the root scroll
+// layer's coordinate space.
+class TopControlsAnimation {
+ public:
+  // Construct with the state at the beginning of the animation.
+  static scoped_ptr<TopControlsAnimation> Create(float start_y_offset,
+                                                 float top_controls_height,
+                                                 base::TimeTicks start_time,
+                                                 base::TimeDelta max_duration);
+
+  ~TopControlsAnimation();
+
+  void SetDirection(bool showing);
+
+  // Call these functions while the animation is in progress to output the
+  // current state.
+  float ScrollOffsetAtTime(base::TimeTicks time) const;
+  bool IsAnimationCompleteAtTime(base::TimeTicks time) const;
+
+ protected:
+  TopControlsAnimation(float start_y_offset,
+                       float top_controls_height,
+                       base::TimeTicks start_time,
+                       base::TimeDelta max_duration);
+
+ private:
+  scoped_ptr<TimingFunction> timing_function_;
+  const float top_controls_height_;
+  const float start_y_offset_;
+  const base::TimeTicks start_time_;
+  const base::TimeDelta max_duration_;
+  int direction_;
+};
+
+}  // namespace cc
+
+#endif  // CC_TOP_CONTROLS_ANIMATION_H_