Fix use-after-free in WidgetCaptureTest.SetCaptureToNonToplevel.

ui/views/widget/widget_interactive_uitest.cc

Index: ui/views/widget/widget_interactive_uitest.cc
diff --git a/ui/views/widget/widget_interactive_uitest.cc b/ui/views/widget/widget_interactive_uitest.cc
index 8fa88e7ca73281129e5062de4704bdb08619c19c..3986ee4ea721e21b46f35ec9dfeb43b990a96d1f 100644
--- a/ui/views/widget/widget_interactive_uitest.cc
+++ b/ui/views/widget/widget_interactive_uitest.cc
@@ -1557,6 +1557,8 @@ TEST_F(WidgetCaptureTest, SetCaptureToNonToplevel) {
 
   EXPECT_TRUE(observer.activation_observed());
   EXPECT_TRUE(child->HasCapture());
+
+  child->RemoveObserver(&observer);
 }