MacViews: Hide windows before closing.

ui/views/cocoa/bridged_native_widget.mm

Index: ui/views/cocoa/bridged_native_widget.mm
diff --git a/ui/views/cocoa/bridged_native_widget.mm b/ui/views/cocoa/bridged_native_widget.mm
index ce3731d026165eb42ef39e0b00bafe6953e2fcf9..7fdc5f342792acb8c9b9e3749c32f2965210b79d 100644
--- a/ui/views/cocoa/bridged_native_widget.mm
+++ b/ui/views/cocoa/bridged_native_widget.mm
@@ -363,6 +363,8 @@ NSUInteger CountBridgedWindows(NSArray* child_windows) {
   DCHECK(child_windows_.empty());
   SetFocusManager(nullptr);
   SetRootView(nullptr);
+
+  DCHECK(![window_ isVisible]);
   DestroyCompositor();
 }
 
@@ -681,6 +683,11 @@ NSUInteger CountBridgedWindows(NSArray* child_windows) {
 }
 
 void BridgedNativeWidget::OnWindowWillClose() {
+  // Hide the window before closing. This ensures that destroying the compositor
+  // during the close does not cause a flash, which would be the case if the
+  // window was still visible.
+  SetVisibilityState(HIDE_WINDOW);
+
   native_widget_mac_->GetWidget()->OnNativeWidgetDestroying();
 
   // Ensure BridgedNativeWidget does not have capture, otherwise