[MD] Don't use new OTR native-theming when using a custom browser theme.

ui/views/widget/widget.cc

Index: ui/views/widget/widget.cc
diff --git a/ui/views/widget/widget.cc b/ui/views/widget/widget.cc
index 895b5e1f903b56962e21e3e428dde0ff3184f7b7..88a68dad587ba9335b3ceeff9c14a641e6b1f2f5 100644
--- a/ui/views/widget/widget.cc
+++ b/ui/views/widget/widget.cc
@@ -129,7 +129,6 @@ Widget::InitParams::InitParams(Type type)
       show_state(ui::SHOW_STATE_DEFAULT),
       parent(nullptr),
       native_widget(nullptr),
-      native_theme(nullptr),
       desktop_window_tree_host(nullptr),
       layer_type(ui::LAYER_TEXTURED),
       context(nullptr),
@@ -145,7 +144,6 @@ Widget::InitParams::~InitParams() {
 
 Widget::Widget()
     : native_widget_(nullptr),
-      native_theme_(nullptr),
       widget_delegate_(nullptr),
       non_client_view_(nullptr),
       dragged_view_(nullptr),
@@ -346,7 +344,6 @@ void Widget::Init(const InitParams& in_params) {
         internal::NativeWidgetPrivate::IsMouseButtonDown();
   }
   native_widget_->InitNativeWidget(params);
-  native_theme_ = params.native_theme;
   if (RequiresNonClientView(params.type)) {
     non_client_view_ = new NonClientView;
     non_client_view_->SetFrameView(CreateNonClientFrameView());
@@ -751,7 +748,7 @@ const ui::ThemeProvider* Widget::GetThemeProvider() const {
 }
 
 const ui::NativeTheme* Widget::GetNativeTheme() const {
-  return native_theme_? native_theme_ : native_widget_->GetNativeTheme();
+  return native_widget_->GetNativeTheme();
 }
 
 FocusManager* Widget::GetFocusManager() {