Update Windows UI on system color changes.

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 8cb845cc3069a2459d29dc4f035b3a309c85f22e..94a1eeff98c54256ac86e70ea410159e60e52c99 100644
--- a/ui/native_theme/native_theme.cc
+++ b/ui/native_theme/native_theme.cc
@@ -4,6 +4,8 @@
 
 #include "ui/native_theme/native_theme.h"
 
+#include "ui/native_theme/native_theme_observer.h"
+
 namespace ui {
 
 void NativeTheme::SetScrollbarColors(unsigned inactive_color,
@@ -17,6 +19,19 @@ void NativeTheme::SetScrollbarColors(unsigned inactive_color,
 // NativeTheme::instance() is implemented in the platform specific source files,
 // such as native_theme_win.cc or native_theme_linux.cc
 
+void NativeTheme::AddObserver(NativeThemeObserver* observer) {
+  native_theme_observers_.AddObserver(observer);
+}
+
+void NativeTheme::RemoveObserver(NativeThemeObserver* observer) {
+  native_theme_observers_.RemoveObserver(observer);
+}
+
+void NativeTheme::NotifyObservers() {
+  FOR_EACH_OBSERVER(NativeThemeObserver, native_theme_observers_,
+                    OnNativeThemeUpdated(this));
+}
+
 NativeTheme::NativeTheme()
     : thumb_inactive_color_(0xeaeaea),
       thumb_active_color_(0xf4f4f4),