ozone/wayland: tabdrag: Switch to null drag icon surface

Now that SwayWM supports null drag icon surfaces to be passed when
starting DND sessions [1], we can safely use it instead of allocating a
surface with no buffer attached, which is currently not supported by
Exosphere [2].

A non-null drag icon surface will be used in the future, once (at least)
Exo supports the protocol extensions being proposed at the tab dragging
design document [3]. This does not cause any functional change.

The aforementioned Sway fix is available for now only in upstream
development branch. It is expected to be included in releases >= 1.5.

[1] https://github.com/swaywm/sway/issues/5509
[2] https://bugs.chromium.org/p/chromium/issues/detail?id=1102926
[3] https://docs.google.com/document/d/1s6OwTi_WC-pS21WLGQYI39yw2m42ZlVolUXBclljXB4/edit?usp=sharing

R=tonikitoo@igalia.com

Bug: 896640
Change-Id: Ic00b960c44c67a2311282b5b46a7cac752a773e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2284981
Commit-Queue: Nick Yamane <nickdiego@igalia.com>
Reviewed-by: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#786013}

ui/ozone/platform/wayland/host/wayland_window_drag_controller.cc

@@ -194,7 +194,6 @@ void WaylandWindowDragController::OnDataSourceFinish(bool completed) {
   // Release DND objects.
   data_offer_.reset();
   data_source_.reset();
-  icon_surface_.reset();
   origin_surface_.reset();
   origin_window_ = nullptr;
   dragged_window_ = nullptr;
@@ -255,9 +254,6 @@ bool WaylandWindowDragController::OfferWindow() {
     data_source_ = data_device_manager_->CreateSource(this);
 
   if (state_ == State::kIdle) {
-    DCHECK(!icon_surface_);
-    icon_surface_ = connection_->CreateSurface();
-
     // Observe window so we can take ownership of the origin surface in case it
     // is destroyed during the DND session.
     window_manager_->AddObserver(this);
@@ -266,8 +262,11 @@ bool WaylandWindowDragController::OfferWindow() {
     state_ = State::kAttached;
     data_source_->Offer({kMimeTypeChromiumWindow});
     data_source_->SetAction(DragDropTypes::DRAG_MOVE);
-    data_device_->StartDrag(*data_source_, *origin_window_, icon_surface_.get(),
-                            this);
+
+    // TODO(crbug.com/1099418): Use dragged window's surface as icon surface
+    // once "immediate drag" protocol extensions are available.
+    data_device_->StartDrag(*data_source_, *origin_window_,
+                            /*icon_surface=*/nullptr, this);
   }
 
   pointer_grab_owner_ = origin_window_;

ui/ozone/platform/wayland/host/wayland_window_drag_controller.h

@@ -113,7 +113,6 @@ class WaylandWindowDragController : public WaylandDataDevice::DragDelegate,
 
   std::unique_ptr<WaylandDataSource> data_source_;
   std::unique_ptr<WaylandDataOffer> data_offer_;
-  wl::Object<wl_surface> icon_surface_;
 
   // The current toplevel window being dragged, when in detached mode.
   WaylandToplevelWindow* dragged_window_ = nullptr;