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

ui/views/controls/menu/menu_host.cc

Index: ui/views/controls/menu/menu_host.cc
diff --git a/ui/views/controls/menu/menu_host.cc b/ui/views/controls/menu/menu_host.cc
index c6750a6e0cd51be18d9470a45969bed6b27c0e4c..b16cfe223a7c8d50c1274e1350d65a4d1bddbc72 100644
--- a/ui/views/controls/menu/menu_host.cc
+++ b/ui/views/controls/menu/menu_host.cc
@@ -80,6 +80,14 @@ class PreMenuEventDispatchHandler : public ui::EventHandler,
 };
 #endif  // OS_MACOSX
 
+#if !defined(OS_MACOSX)
+void TransferGesture(Widget* source, Widget* target) {

[msw, 2017/05/17 23:03:30]

nit: comment, maybe seek menu review from sky@?

+  ui::GestureRecognizer::Get()->TransferEventsTo(
+      source->GetNativeView(), target->GetNativeView(),
+      ui::GestureRecognizer::ShouldCancelTouches::DontCancel);
+}
+#endif
+
 }  // namespace internal
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -125,6 +133,7 @@ void MenuHost::InitMenuHost(Widget* parent,
 #if !defined(OS_MACOSX)
   pre_dispatch_handler_.reset(new internal::PreMenuEventDispatchHandler(
       menu_controller, submenu_, GetNativeView()));
+  owner_ = parent;
 #endif
 
   SetContentsView(contents_view);
@@ -143,12 +152,36 @@ void MenuHost::ShowMenuHost(bool do_capture) {
   if (do_capture) {
     // Cancel existing touches, so we don't miss some touch release/cancel

[msw, 2017/05/17 23:03:30]

nit: move comment into else?

[minch1, 2017/05/26 23:01:12]

Done.

     // events due to the menu taking capture.
+#if !defined(OS_MACOSX)
+    MenuController* menu_controller =
+        submenu_->GetMenuItem()->GetMenuController();
+    if (menu_controller) {
+      if (menu_controller->owner_needs_gesture_events()) {
+        // TransferGesture when owner needs gesture events so that the incoming
+        // touch events after MenuHost is created are properly translated into
+        // gesture events instead of being dropped.
+        internal::TransferGesture(owner_, this);
+      } else {
+        ui::GestureRecognizer::Get()->CancelActiveTouchesExcept(nullptr);
+      }
+    }
+#else
     ui::GestureRecognizer::Get()->CancelActiveTouchesExcept(nullptr);
+#endif
     native_widget_private()->SetCapture();
   }
 }
 
 void MenuHost::HideMenuHost() {
+#if !defined(OS_MACOSX)
+  MenuController* menu_controller =
+      submenu_->GetMenuItem()->GetMenuController();
+  if (owner_ && menu_controller &&
+      menu_controller->owner_needs_gesture_events()) {
+    internal::TransferGesture(this, owner_);
+    owner_ = nullptr;
+  }
+#endif
   ignore_capture_lost_ = true;
   ReleaseMenuHostCapture();
   Hide();