Avoid DefWindowProc non-client rendering over our custom frame.

views/widget/native_widget_win.cc

Index: views/widget/native_widget_win.cc
diff --git a/views/widget/native_widget_win.cc b/views/widget/native_widget_win.cc
index 1afcb415b3385da5c65aa00bd830a673345eb37f..9290f4b21a84d80ae2592444b579620c71f1e022 100644
--- a/views/widget/native_widget_win.cc
+++ b/views/widget/native_widget_win.cc
@@ -1186,9 +1186,9 @@ void NativeWidgetWin::OnActivateApp(BOOL active, DWORD thread_id) {
     // Another application was activated, we should reset any state that
     // disables inactive rendering now.
     delegate_->EnableInactiveRendering();
-    // Update the native frame too, since it could be rendering the non-client
-    // area.
-    DefWindowProcWithRedrawLock(WM_NCACTIVATE, FALSE, 0);
+    // Also update the native frame if it is rendering the non-client area.
+    if (GetWidget()->ShouldUseNativeFrame())
+      DefWindowProcWithRedrawLock(WM_NCACTIVATE, FALSE, 0);
   }
 }
 
@@ -1626,6 +1626,12 @@ LRESULT NativeWidgetWin::OnNCActivate(BOOL active) {
   if (IsActive())
     delegate_->EnableInactiveRendering();
 
+  // Avoid DefWindowProc non-client rendering over our custom frame.
+  if (!GetWidget()->ShouldUseNativeFrame()) {
+    SetMsgHandled(TRUE);
+    return TRUE;
+  }
+
   return DefWindowProcWithRedrawLock(WM_NCACTIVATE,
                                      inactive_rendering_disabled || active, 0);
 }