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) {
+    part.submenu->OnGestureEvent(event);
     return;
-  part.submenu->OnGestureEvent(event);
+  }
+
+#if !defined(OS_MACOSX)
+  if (owner_needs_gesture_events()) {
+    event->ConvertLocationToTarget(source->GetWidget()->GetNativeWindow(),
+                                   owner()->GetNativeWindow());
+    owner()->OnGestureEvent(event);
+    // Don't transfer events back if capture the GESTURE_END. Then the following
+    // gesture events on the shelf can be created correctly.

[xiyuan, 2017/05/26 23:13:37]

Think it would be easier to understand if we rename owner_needs_gesture_events_
etc to prevserve_current_gesture_for_owner_.

Then this comment can be something like:
  // Reset |prevserve_current_gesture_for_owner_| flag when the current
  // gesture ends.

[minch1, 2017/06/01 16:42:28]

Done.

+    if (event->type() == ui::ET_GESTURE_END)
+      set_owner_needs_gesture_events(false);
+  }
+#endif  // !defined(OS_MACOSX)
 }
 
 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 533 matching lines @@
 #endif
 
     default:
       break;
   }
 }
 
 MenuController::MenuController(bool blocking,
                                internal::MenuControllerDelegate* delegate)
     : blocking_run_(blocking),
-      showing_(false),
-      exit_type_(EXIT_NONE),
-      did_capture_(false),
-      result_(NULL),
-      accept_event_flags_(0),
-      drop_target_(NULL),
-      drop_position_(MenuDelegate::DROP_UNKNOWN),
-      owner_(NULL),
-      possible_drag_(false),
-      drag_in_progress_(false),
-      did_initiate_drag_(false),
-      valid_drop_coordinates_(false),
-      last_drop_operation_(MenuDelegate::DROP_UNKNOWN),
-      showing_submenu_(false),
       active_mouse_view_id_(ViewStorage::GetInstance()->CreateStorageID()),
-      hot_button_(nullptr),
-      delegate_(delegate),
-      is_combobox_(false),
-      item_selected_by_touch_(false),
-      current_mouse_event_target_(nullptr),
-      current_mouse_pressed_state_(0) {
+      delegate_(delegate) {
   delegate_stack_.push_back(delegate_);
   active_instance_ = this;
 }
 
 MenuController::~MenuController() {
   DCHECK(!showing_);
   if (owner_)
     owner_->RemoveObserver(this);
   if (active_instance_ == this)
     active_instance_ = NULL;
@@ skipping 1304 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