Update the gesture target on AttemptToStartDrag.

For Exo windows, the initial gesture target is set to an ExoSurface. If
the client (Android) requests a drag-move or drag-resize, then Exo calls
AttemptToStartDrag, and provides the ExoShellSurface as the target.
Then, ToplevelWindowEventHandler will transfer the events to the new
target. However, WmToplevelWindowEventHandler won't update the gesture
target. This means all events will be ignored later in
WmToplevelWindowEventHandler::OnGestureEvent because it believes they
are events for the client which need to not be delivered.

Bug: b/124026845
Test: Drag-to-move via touch of a PIP window no longer lags.
Change-Id: I6e7bca73561fdab1bf357dd86de2a5d4e9a4bddc
Reviewed-on: https://chromium-review.googlesource.com/c/1477452Reviewed-by: Eliot Courtney <edcourtney@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634401}

ash/wm/toplevel_window_event_handler.cc

@@ -51,13 +51,9 @@ bool ToplevelWindowEventHandler::AttemptToStartDrag(
   ::wm::WindowMoveSource source = gesture_target
                                       ? ::wm::WINDOW_MOVE_SOURCE_TOUCH
                                       : ::wm::WINDOW_MOVE_SOURCE_MOUSE;
-  if (gesture_target) {
-    window->env()->gesture_recognizer()->TransferEventsTo(
-        gesture_target, window, ui::TransferTouchesBehavior::kDontCancel);
-  }
   return wm_toplevel_window_event_handler_.AttemptToStartDrag(
-      window, point_in_parent, window_component, source,
-      std::move(end_closure));
+      window, point_in_parent, window_component, source, std::move(end_closure),
+      /*update_gesture_target=*/true);
 }
 
 ::wm::WindowMoveResult ToplevelWindowEventHandler::RunMoveLoop(
@@ -96,7 +92,8 @@ bool ToplevelWindowEventHandler::AttemptToStartDrag(
   if (!wm_toplevel_window_event_handler_.AttemptToStartDrag(
           source, drag_location, HTCAPTION, move_source,
           base::Bind(&ToplevelWindowEventHandler::OnDragCompleted,
-                     weak_factory_.GetWeakPtr(), &result, &run_loop))) {
+                     weak_factory_.GetWeakPtr(), &result, &run_loop),
+          /*update_gesture_target=*/false)) {
     return ::wm::MOVE_CANCELED;
   }
 

ash/wm/wm_toplevel_window_event_handler.cc

@@ -376,7 +376,8 @@ void WmToplevelWindowEventHandler::OnGestureEvent(ui::GestureEvent* event,
         if (CanStartTwoFingerMove(target, first_finger_hittest_,
                                   second_finger_hittest)) {
           AttemptToStartDrag(target, first_finger_touch_point_, HTCAPTION,
-                             ::wm::WINDOW_MOVE_SOURCE_TOUCH, EndClosure());
+                             ::wm::WINDOW_MOVE_SOURCE_TOUCH, EndClosure(),
+                             /*update_gesture_target=*/false);
           event->StopPropagation();
         }
       }
@@ -398,7 +399,8 @@ void WmToplevelWindowEventHandler::OnGestureEvent(ui::GestureEvent* event,
       aura::Window::ConvertPointToTarget(target, target->parent(),
                                          &location_in_parent);
       AttemptToStartDrag(target, location_in_parent, component,
-                         ::wm::WINDOW_MOVE_SOURCE_TOUCH, EndClosure());
+                         ::wm::WINDOW_MOVE_SOURCE_TOUCH, EndClosure(),
+                         /*update_gesture_target=*/false);
       event->StopPropagation();
       return;
     }
@@ -461,7 +463,8 @@ bool WmToplevelWindowEventHandler::AttemptToStartDrag(
     const gfx::Point& point_in_parent,
     int window_component,
     ::wm::WindowMoveSource source,
-    EndClosure end_closure) {
+    EndClosure end_closure,
+    bool update_gesture_target) {
   if (!PrepareForDrag(window, point_in_parent, window_component, source)) {
     // Treat failure to start as a revert.
     if (end_closure)
@@ -473,8 +476,14 @@ bool WmToplevelWindowEventHandler::AttemptToStartDrag(
   in_gesture_drag_ = (source == ::wm::WINDOW_MOVE_SOURCE_TOUCH);
   // |gesture_target_| needs to be updated if the drag originated from a
   // client (i.e. |this| never handled ET_GESTURE_EVENT_BEGIN).
-  if (in_gesture_drag_ && !gesture_target_)
+  if (in_gesture_drag_ && (!gesture_target_ || update_gesture_target)) {
+    if (gesture_target_ && gesture_target_ != window) {
+      // Transfer events for gesture if switching to new target.
+      window->env()->gesture_recognizer()->TransferEventsTo(
+          gesture_target_, window, ui::TransferTouchesBehavior::kDontCancel);
+    }
     UpdateGestureTarget(window);
+  }
 
   return true;
 }
@@ -543,7 +552,8 @@ void WmToplevelWindowEventHandler::HandleMousePressed(aura::Window* target,
     aura::Window::ConvertPointToTarget(target, target->parent(),
                                        &location_in_parent);
     AttemptToStartDrag(target, location_in_parent, component,
-                       ::wm::WINDOW_MOVE_SOURCE_MOUSE, EndClosure());
+                       ::wm::WINDOW_MOVE_SOURCE_MOUSE, EndClosure(),
+                       /*update_gesture_target=*/false);
     // Set as handled so that other event handlers do no act upon the event
     // but still receive it so that they receive both parts of each pressed/
     // released pair.

ash/wm/wm_toplevel_window_event_handler.h

@@ -67,12 +67,15 @@ class ASH_EXPORT WmToplevelWindowEventHandler
 
   // Attempts to start a drag if one is not already in progress. Returns true if
   // successful. |end_closure| is run when the drag completes, including if the
-  // drag is not started.
+  // drag is not started. If |update_gesture_target| is true, the gesture
+  // target is forcefully updated and gesture events are transferred to
+  // new target if any.
   bool AttemptToStartDrag(aura::Window* window,
                           const gfx::Point& point_in_parent,
                           int window_component,
                           ::wm::WindowMoveSource source,
-                          EndClosure end_closure);
+                          EndClosure end_closure,
+                          bool update_gesture_target);
 
   // If there is a drag in progress it is reverted, otherwise does nothing.
   void RevertDrag();

ash/ws/window_service_delegate_impl.cc

@@ -137,7 +137,8 @@ void WindowServiceDelegateImpl::RunWindowMoveLoop(
       ->wm_toplevel_window_event_handler()
       ->AttemptToStartDrag(
           window, location_in_parent, window_component, aura_source,
-          base::BindOnce(&OnMoveLoopCompleted, std::move(callback)));
+          base::BindOnce(&OnMoveLoopCompleted, std::move(callback)),
+          /*update_gesture_target=*/false);
 }
 
 void WindowServiceDelegateImpl::CancelWindowMoveLoop() {