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..48d262ba837cf69788fceee7943837c5e7f6985a 100644
--- a/ui/views/controls/menu/menu_host.cc
+++ b/ui/views/controls/menu/menu_host.cc
@@ -12,7 +12,6 @@
 #include "ui/events/gestures/gesture_recognizer.h"
 #include "ui/gfx/path.h"
 #include "ui/native_theme/native_theme.h"
-#include "ui/views/controls/menu/menu_controller.h"
 #include "ui/views/controls/menu/menu_host_root_view.h"
 #include "ui/views/controls/menu/menu_item_view.h"
 #include "ui/views/controls/menu/menu_scroll_view_container.h"
@@ -82,6 +81,18 @@ class PreMenuEventDispatchHandler : public ui::EventHandler,
 
 }  // namespace internal
 
+namespace {
+
+#if defined(OS_CHROMEOS)
+void TransferGesture(Widget* source, Widget* target) {
+  ui::GestureRecognizer::Get()->TransferEventsTo(
+      source->GetNativeView(), target->GetNativeView(),
+      ui::GestureRecognizer::ShouldCancelTouches::DontCancel);
+}
+#endif
+
+}  // namespace

[xiyuan, 2017/05/16 22:46:57]

nit: We probably can put TransferGesture in the internal namespace above.

[minch1, 2017/05/17 16:55:38]

Done.

+
 ////////////////////////////////////////////////////////////////////////////////
 // MenuHost, public:
 
@@ -127,6 +138,13 @@ void MenuHost::InitMenuHost(Widget* parent,
       menu_controller, submenu_, GetNativeView()));
 #endif
 
+#if defined(OS_CHROMEOS)

[xiyuan, 2017/05/16 22:46:57]

I wonder whether we should consider !defined(OS_MACOSX) instead of
defined(OS_CHROMEOS). The code probably can work on win/linux since those are
aura based too.

+  if (parent && controller && controller->owner_needs_gesture_events()) {

[xiyuan, 2017/05/16 22:46:57]

Briefly document why we need to TransferGesture.

  // 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.

[minch1, 2017/05/17 16:55:37]

Done.

+    owner_ = parent;
+    TransferGesture(owner_, this);

[xiyuan, 2017/05/16 22:46:57]

Can we move this to ShowMenuHost so that it is symmetric with the
TransferGesture in HideMenuHost?

[minch1, 2017/05/17 16:55:37]

Done.

+  }
+#endif
+
   SetContentsView(contents_view);
   ShowMenuHost(do_capture);
 }
@@ -143,12 +161,24 @@ void MenuHost::ShowMenuHost(bool do_capture) {
   if (do_capture) {
     // Cancel existing touches, so we don't miss some touch release/cancel
     // events due to the menu taking capture.
+#if defined(OS_CHROMEOS)
+    if (controller && !controller->owner_needs_gesture_events())
+      ui::GestureRecognizer::Get()->CancelActiveTouchesExcept(nullptr);
+#else
     ui::GestureRecognizer::Get()->CancelActiveTouchesExcept(nullptr);
+#endif
     native_widget_private()->SetCapture();
   }
 }
 
 void MenuHost::HideMenuHost() {
+#if defined(OS_CHROMEOS)
+  if (owner_ && controller && controller->owner_needs_gesture_events()) {
+    TransferGesture(this, owner_);
+    owner_ = nullptr;
+    controller->set_owner_needs_gesture_events(false);

[xiyuan, 2017/05/16 22:46:57]

Do we still need this after making the flag a member of controller?

[minch1, 2017/05/17 16:55:38]

Oh, yeap, we don't need to do this.

+  }
+#endif
   ignore_capture_lost_ = true;
   ReleaseMenuHostCapture();
   Hide();