Update which window the mouse is physically on

This fixes the regression in crrev.com/c/1826666.

Bug: 1019737
Test: covered by unittest
Change-Id: I45401bb8c482d763991ca34f51537f2a5a6889e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1893511
Auto-Submit: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: kylechar <kylechar@chromium.org>
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711786}

ui/ozone/platform/x11/x11_window_ozone_unittest.cc

@@ -248,10 +248,22 @@ TEST_F(X11WindowOzoneTest, MouseEnterAndDelete) {
   EXPECT_CALL(delegate_2, OnMouseEnter()).Times(1);
   window_manager()->MouseOnWindow(static_cast<X11WindowOzone*>(window_2.get()));
 
-  // Removing the window should reset the |window_mouse_currently_on_|.
   EXPECT_EQ(window_2.get(),
             window_manager()->window_mouse_currently_on_for_test());
-  window_2.reset();
+
+  // Dispatch Event on window 1 while event is captured on window 2.
+  ::testing::Mock::VerifyAndClearExpectations(&delegate_1);
+  EXPECT_CALL(delegate_1, OnMouseEnter()).Times(1);
+  window_2->SetCapture();
+  ScopedXI2Event xi_event;
+  xi_event.InitGenericButtonEvent(kPointerDeviceId, ET_MOUSE_PRESSED,
+                                  gfx::Point(0, 0), EF_NONE);
+  DispatchXEvent(xi_event, widget_1);
+  EXPECT_EQ(window_1.get(),
+            window_manager()->window_mouse_currently_on_for_test());
+
+  // Removing the window should reset the |window_mouse_currently_on_|.
+  window_1.reset();
   EXPECT_FALSE(window_manager()->window_mouse_currently_on_for_test());
 }
 

ui/platform_window/x11/x11_window.cc

@@ -476,6 +476,13 @@ uint32_t X11Window::DispatchEvent(const PlatformEvent& event) {
     ProcessEvent(event);
   return POST_DISPATCH_STOP_PROPAGATION;
 #else
+  // Notify that the mouse gets physically entered to the window regardless of
+  // the grab. This is used to update the mouse cursor state.
+  auto* window_manager = X11WindowManager::GetInstance();
+  DCHECK(window_manager);
+  if (event->IsMouseEvent())
+    window_manager->MouseOnWindow(this);
+
   OnXWindowEvent(event);
   return POST_DISPATCH_STOP_PROPAGATION;
 #endif
@@ -565,9 +572,6 @@ void X11Window::OnXWindowEvent(ui::Event* event) {
     return;
   }
 
-  if (event->IsMouseEvent())
-    window_manager->MouseOnWindow(this);
-
 #if defined(USE_OZONE)
   DispatchEventFromNativeUiEvent(
       event, base::BindOnce(&PlatformWindowDelegate::DispatchEvent,