Make shelf item can be dragged when context menu is opened.

ui/views/controls/menu/submenu_view.cc

 // Copyright (c) 2012 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.
 
 #include "ui/views/controls/menu/submenu_view.h"
 
 #include <algorithm>
 
 #include "base/compiler_specific.h"
 #include "ui/accessibility/ax_node_data.h"
@@ skipping 349 matching lines @@
 base::string16 SubmenuView::GetTextForRow(int row) {
   return GetMenuItemAt(row)->title();
 }
 
 bool SubmenuView::IsShowing() {
   return host_ && host_->IsMenuHostVisible();
 }
 
 void SubmenuView::ShowAt(Widget* parent,
                          const gfx::Rect& bounds,
-                         bool do_capture) {
+                         bool do_capture,
+                         bool cancel_active_touches) {

[xiyuan, 2017/05/12 20:24:57]

ditto, get |cancel_active_touches| from MenuController ?

   if (host_) {
-    host_->ShowMenuHost(do_capture);
+    host_->ShowMenuHost(do_capture, cancel_active_touches);
   } else {
     host_ = new MenuHost(this);
     // Force construction of the scroll view container.
     GetScrollViewContainer();
     // Force a layout since our preferred size may not have changed but our
     // content may have.
     InvalidateLayout();
-    host_->InitMenuHost(parent, bounds, scroll_view_container_, do_capture);
+    host_->InitMenuHost(parent, bounds, scroll_view_container_, do_capture,
+                        cancel_active_touches);
   }
 
   GetScrollViewContainer()->NotifyAccessibilityEvent(
       ui::AX_EVENT_MENU_START,
       true);
   NotifyAccessibilityEvent(
       ui::AX_EVENT_MENU_POPUP_START,
       true);
 }
 
@@ skipping 123 matching lines @@
   y = std::max(y, 0);
   gfx::Rect new_vis_bounds(x, y, vis_bounds.width(), vis_bounds.height());
   if (new_vis_bounds != vis_bounds) {
     ScrollRectToVisible(new_vis_bounds);
     return true;
   }
   return false;
 }
 
 }  // namespace views