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

ui/views/controls/menu/menu_controller.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/menu_controller.h"
 
 #include "base/i18n/case_conversion.h"
 #include "base/i18n/rtl.h"
 #include "base/macros.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 802 matching lines @@
     // current menu is unset. Make sure the submenu remains open by sending the
     // appropriate SetSelectionTypes flags.
     SetSelection(part.menu->GetParentMenuItem(),
         SELECTION_OPEN_SUBMENU | SELECTION_UPDATE_IMMEDIATELY);
     event->StopPropagation();
   }
 
   if (event->stopped_propagation())
       return;
 
-  if (!part.submenu)
+  if (!part.submenu) {
+    event->ConvertLocationToTarget(source->GetWidget()->GetNativeWindow(),
+                                   owner()->GetNativeWindow());
+    owner()->OnGestureEvent(event);
     return;
+  }

[xiyuan, 2017/05/12 20:24:56]

nit: revist to something like

if (part.submenu) {
  part.submenu->OnGestureEvent(event);
  return;
}

// Forwarding to owner if necessary. We might want to use
// |cancel_active_touches_| as a flag as whether to do the
// forwarding.

   part.submenu->OnGestureEvent(event);
 }
 
 void MenuController::OnTouchEvent(SubmenuView* source, ui::TouchEvent* event) {
   if (event->type() == ui::ET_TOUCH_PRESSED) {
     MenuPart part = GetMenuPart(source, event->location());
     if (part.type == MenuPart::NONE) {
       RepostEventAndCancel(source, event);
       event->SetHandled();
     }
@@ skipping 982 matching lines @@
   gfx::Rect bounds = MenuItemView::IsBubble(state_.anchor) ?
       CalculateBubbleMenuBounds(item, prefer_leading, &resulting_direction) :
       CalculateMenuBounds(item, prefer_leading, &resulting_direction);
   state_.open_leading.push_back(resulting_direction);
   bool do_capture = (!did_capture_ && blocking_run_);
   showing_submenu_ = true;
   if (show) {
     // Menus are the only place using kGroupingPropertyKey, so any value (other
     // than 0) is fine.
     const int kGroupingId = 1001;
-    item->GetSubmenu()->ShowAt(owner_, bounds, do_capture);
+    item->GetSubmenu()->ShowAt(owner_, bounds, do_capture,
+                               cancel_active_touches_);
     item->GetSubmenu()->GetWidget()->SetNativeWindowProperty(
         TooltipManager::kGroupingPropertyKey,
         reinterpret_cast<void*>(kGroupingId));
   } else {
     item->GetSubmenu()->Reposition(bounds);
   }
   showing_submenu_ = false;
 }
 
 void MenuController::MenuChildrenChanged(MenuItemView* item) {
@@ skipping 876 matching lines @@
   if (hot_button_)
     hot_button_->SetHotTracked(false);
   hot_button_ = hot_button;
   if (hot_button) {
     hot_button->SetHotTracked(true);
     hot_button->NotifyAccessibilityEvent(ui::AX_EVENT_SELECTION, true);
   }
 }
 
 }  // namespace views