Add gesture support in views::ResizeArea

ui/views/controls/resize_area.h

 // Copyright (c) 2011 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_VIEWS_CONTROLS_RESIZE_AREA_H_
 #define UI_VIEWS_CONTROLS_RESIZE_AREA_H_
 
 #include <string>
 
 #include "base/macros.h"
 #include "ui/views/view.h"
 
 namespace views {
 
 class ResizeAreaDelegate;
 
-////////////////////////////////////////////////////////////////////////////////
-//
 // An invisible area that acts like a horizontal resizer.
-//
-////////////////////////////////////////////////////////////////////////////////
 class VIEWS_EXPORT ResizeArea : public View {
  public:
   static const char kViewClassName[];
 
   explicit ResizeArea(ResizeAreaDelegate* delegate);
   ~ResizeArea() override;
 
-  // Overridden from views::View:
+  // views::View:
   const char* GetClassName() const override;
   gfx::NativeCursor GetCursor(const ui::MouseEvent& event) override;
+  void OnGestureEvent(ui::GestureEvent* event) override;
   bool OnMousePressed(const ui::MouseEvent& event) override;
   bool OnMouseDragged(const ui::MouseEvent& event) override;
   void OnMouseReleased(const ui::MouseEvent& event) override;
   void OnMouseCaptureLost() override;
   void GetAccessibleNodeData(ui::AXNodeData* node_data) override;
 
  private:
   // Report the amount the user resized by to the delegate, accounting for
   // directionality.
   void ReportResizeAmount(int resize_amount, bool last_update);
 
+  // Converts |event_x| to screen coordinates and sets |initial_position_| to
+  // this value.
+  void SetInitialPosition(int event_x);
+
   // The delegate to notify when we have updates.
   ResizeAreaDelegate* delegate_;
 
-  // The mouse position at start (in screen coordinates).
+  // The event's x-position at the start of the resize operation. The resize
+  // area will move while being dragged, so |initial_position_| is represented
+  // in screen coordinates so that we don't lose our bearings.
   int initial_position_;
 
   DISALLOW_COPY_AND_ASSIGN(ResizeArea);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_RESIZE_AREA_H_