Change name of NativeTheme::instance() to make it clear it's web only.

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc

Index: ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
diff --git a/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc b/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
index d02dede8a7569828789be42e5724717dd6c3940d..81b250bd834557800989ebb08c33d2b51d916fa8 100644
--- a/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
+++ b/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
@@ -40,6 +40,7 @@
 #include "ui/gfx/path_x11.h"
 #include "ui/gfx/screen.h"
 #include "ui/native_theme/native_theme.h"
+#include "ui/native_theme/native_theme_aura.h"
 #include "ui/views/corewm/tooltip_aura.h"
 #include "ui/views/linux_ui/linux_ui.h"
 #include "ui/views/views_delegate.h"
@@ -2069,7 +2070,7 @@ ui::NativeTheme* DesktopWindowTreeHost::GetNativeTheme(aura::Window* window) {
       return native_theme;
   }
 
-  return ui::NativeTheme::instance();
+  return ui::NativeThemeAura::instance();
 }
 
 }  // namespace views