Add VectorIconButton functionality to ImageButton.

ui/views/view_observer.h

Index: ui/views/view_observer.h
diff --git a/ui/views/view_observer.h b/ui/views/view_observer.h
index c1d69f92cc313e4d73fdb4b6b1124a54ef588e50..745c9f275a0fc8fa52e0921dedceff488619a35f 100644
--- a/ui/views/view_observer.h
+++ b/ui/views/view_observer.h
@@ -7,6 +7,10 @@
 
 #include "ui/views/views_export.h"
 
+namespace ui {
+class NativeTheme;
+}
+
 namespace views {
 
 class View;
@@ -33,6 +37,10 @@ class VIEWS_EXPORT ViewObserver {
   // parent view. |view| is the child view being moved.
   virtual void OnChildViewReordered(View* view) {}
 
+  virtual void OnThemeChanged(View* view) {}
+
+  virtual void OnNativeThemeChanged(View* view, const ui::NativeTheme* theme) {}
+
  protected:
   virtual ~ViewObserver() {}
 };