Fix expectations for Windows for MouseExitOnCaptureGrab, and re-enable.

On Windows, Chrome doesn't generate a synthetic mouse exit event,
see crbug.com/394672.

Change-Id: I1b8ae0e43061f2c555c317cfd1f2f683b79db738
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2316843
Commit-Queue: David Bienvenu <davidbienvenu@chromium.org>
Reviewed-by: Peter Boström <pbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#793804}

ui/views/widget/widget_interactive_uitest.cc

@@ -1718,14 +1718,15 @@ TEST_F(WidgetCaptureTest, MAYBE_SystemModalWindowReleasesCapture) {
 // Regression test for http://crbug.com/382421 (Linux-Aura issue).
 // TODO(pkotwicz): Make test pass on CrOS and Windows.
 // TODO(tapted): Investigate for toolkit-views on Mac http;//crbug.com/441064.
-#if defined(OS_CHROMEOS) || defined(OS_WIN) || defined(OS_APPLE)
+#if defined(OS_CHROMEOS) || defined(OS_APPLE)
 #define MAYBE_MouseExitOnCaptureGrab DISABLED_MouseExitOnCaptureGrab
 #else
 #define MAYBE_MouseExitOnCaptureGrab MouseExitOnCaptureGrab
 #endif
 
 // Test that a synthetic mouse exit is sent to the widget which was handling
-// mouse events when a different widget grabs capture.
+// mouse events when a different widget grabs capture. Except for Windows,
+// which does not send a synthetic mouse exit.
 TEST_F(WidgetCaptureTest, MAYBE_MouseExitOnCaptureGrab) {
   Widget widget1;
   Widget::InitParams params1 =
@@ -1754,9 +1755,15 @@ TEST_F(WidgetCaptureTest, MAYBE_MouseExitOnCaptureGrab) {
 
   widget2.SetCapture(nullptr);
   EXPECT_EQ(0, mouse_view1->EnteredCalls());
-  // Grabbing native capture on Windows generates a ui::ET_MOUSE_EXITED event
-  // in addition to the one generated by Chrome.
-  EXPECT_LT(0, mouse_view1->ExitedCalls());
+  // On Windows, Chrome doesn't synthesize a separate mouse exited event.
+  // Instead, it uses ::TrackMouseEvent to get notified of the mouse leaving.
+  // Calling SetCapture does not cause Windows to generate a WM_MOUSELEAVE
+  // event. See WindowEventDispatcher::OnOtherRootGotCapture() for more info.
+#if defined(OS_WIN)
+  EXPECT_EQ(0, mouse_view1->ExitedCalls());
+#else
+  EXPECT_EQ(1, mouse_view1->ExitedCalls());
+#endif  // OS_WIN
 }
 
 namespace {