Add more out of line copy ctors for complex classes.

ui/native_theme/native_theme.cc

Index: ui/native_theme/native_theme.cc
diff --git a/ui/native_theme/native_theme.cc b/ui/native_theme/native_theme.cc
index 96b0072ce706ec0501d83581adfef4b2fd164de3..9b2587aaa914b3477907eb7cab1070ae0c106c54 100644
--- a/ui/native_theme/native_theme.cc
+++ b/ui/native_theme/native_theme.cc
@@ -14,6 +14,8 @@ NativeTheme::ExtraParams::ExtraParams() {
   memset(this, 0, sizeof(*this));
 }
 
+NativeTheme::ExtraParams::ExtraParams(const ExtraParams& other) = default;
+
 void NativeTheme::SetScrollbarColors(unsigned inactive_color,
                                      unsigned active_color,
                                      unsigned track_color) {