Support longpress drag selection

ui/touch_selection/touch_selection_draggable.h

Index: ui/touch_selection/touch_selection_draggable.h
diff --git a/ui/touch_selection/touch_selection_draggable.h b/ui/touch_selection/touch_selection_draggable.h
new file mode 100644
index 0000000000000000000000000000000000000000..0bd9a70f8849fc0a245adac8eb8b327cb55bfeb9
--- /dev/null
+++ b/ui/touch_selection/touch_selection_draggable.h
@@ -0,0 +1,43 @@
+// Copyright 2015 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_TOUCH_SELECTION_DRAG_DRAGGABLE_H_
+#define UI_TOUCH_SELECTION_DRAG_DRAGGABLE_H_
+
+#include "ui/gfx/geometry/point_f.h"
+#include "ui/touch_selection/ui_touch_selection_export.h"
+
+namespace ui {
+
+class MotionEvent;
+class TouchSelectionDraggable;
+
+// Interface through which TouchSelectionDraggable manipulates the selection.
+class UI_TOUCH_SELECTION_EXPORT TouchSelectionDraggableClient {
+ public:
+  virtual ~TouchSelectionDraggableClient() {}
+  virtual void OnDragBegin(const TouchSelectionDraggable& draggable,
+                           const gfx::PointF& start_position) = 0;
+  virtual void OnDragUpdate(const TouchSelectionDraggable& draggable,
+                            const gfx::PointF& new_position) = 0;
+  virtual void OnDragEnd(const TouchSelectionDraggable& draggable) = 0;
+  virtual bool IsWithinTapSlop(const gfx::Vector2dF& delta) const = 0;
+};
+
+// Generic interface for entities that manipulate the selection via dragging.
+class UI_TOUCH_SELECTION_EXPORT TouchSelectionDraggable {
+ protected:
+  virtual ~TouchSelectionDraggable() {}
+
+  // Offers a touch sequence to the draggable target. Returns true if the event
+  // was consumed, in which case the caller should cease further handling.
+  virtual bool WillHandleTouchEvent(const ui::MotionEvent& event) = 0;
+
+  // Whether a drag is active OR being detected for the current touch sequence.
+  virtual bool IsActive() const = 0;
+};
+
+}  // namespace ui
+
+#endif  // UI_TOUCH_SELECTION_DRAG_DRAGGABLE_H_