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..26c2f0022b4dfb48d00a843318625823c5ac66fc
--- /dev/null
+++ b/ui/touch_selection/touch_selection_draggable.h
@@ -0,0 +1,35 @@
+// 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;
+};
+
+// Generic interface for entities that manipulate the selection via dragging.
+class UI_TOUCH_SELECTION_EXPORT TouchSelectionDraggable {
+ protected:
+  virtual ~TouchSelectionDraggable() {}

[mfomitchev, 2015/04/23 21:05:53]

Any reason not to add WillHandleTouchEvent to this interface?

[jdduke (slow), 2015/04/27 20:24:25]

Hmm, but what functional purpose would it serve? We'll never use these objects
polymorphically, so it would just be an indicator that these things tend to
handle touch events. I'll make the change anyway I guess.

+};
+
+}  // namespace ui
+
+#endif  // UI_TOUCH_SELECTION_DRAG_DRAGGABLE_H_