Consolidate content fling implementations

ui/events/gesture_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_GESTURE_CURVE_H_
+#define UI_EVENTS_GESTURE_CURVE_H_
+
+#include "base/time/time.h"
+#include "ui/gfx/geometry/vector2d_f.h"
+
+namespace ui {
+
+// An abstraction of curve-based gesture motion, allowing platform-specific
+// motion tailoring.
+class EVENTS_BASE_EXPORT GestureCurve {
+ public:
+  virtual ~GestureCurve() {}
+
+  // The output |offset| represents the total movement of the curve from its
+  // start until |time|.
+  // The output |velocity| represents the instantenous velocity at |time|.
+  // Returns false if |time| exceeds the fling duration, in which case
+  // the terminal offset will be reported.
+  virtual bool ComputeScrollOffset(base::TimeTicks time,
+                                   gfx::Vector2dF* offset,
+                                   gfx::Vector2dF* velocity) = 0;
+};
+
+}  // namespace ui
+
+#endif  // UI_EVENTS_GESTURE_CURVE_H_