athena: Add support for fling-scroll in overview mode.

ui/events/gestures/fling_curve.h

+// Copyright 2014 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 UI_EVENTS_GESTURES_FLING_CURVE_H_
+#define UI_EVENTS_GESTURES_FLING_CURVE_H_
+
+#include "base/time/time.h"
+#include "ui/events/events_base_export.h"
+#include "ui/gfx/geometry/point_f.h"
+#include "ui/gfx/geometry/vector2d_f.h"
+
+namespace ui {
+
+// FlingCurve can be used to scroll a UI element suitable for touch screen-based
+// flings.
+class EVENTS_BASE_EXPORT FlingCurve {
+ public:
+  FlingCurve(const gfx::Vector2dF& velocity, base::TimeTicks start_timestamp);
+  ~FlingCurve();
+
+  gfx::Vector2dF GetScrollAmountAtTime(base::TimeTicks current_timestamp);
+  base::TimeTicks start_timestamp() const { return start_timestamp_; }
+
+ private:
+  const float curve_duration_;
+  const base::TimeTicks start_timestamp_;
+
+  gfx::Vector2dF displacement_ratio_;
+  gfx::Vector2dF cumulative_scroll_;
+  base::TimeTicks last_timestamp_;
+  float time_offset_;
+  float position_offset_;
+
+  DISALLOW_COPY_AND_ASSIGN(FlingCurve);
+};
+
+}  // namespace ui
+
+#endif  // UI_EVENTS_GESTURES_FLING_CURVE_H_