BoxLayout now suports per-view margins.

ui/views/view.h

Index: ui/views/view.h
diff --git a/ui/views/view.h b/ui/views/view.h
index 9f1ca8b509665fda2a4b73d00ff2ffc2fc247acb..9a11e78458c13117b10ba9fa5b4e7aee840a4131 100644
--- a/ui/views/view.h
+++ b/ui/views/view.h
@@ -21,6 +21,7 @@
 #include "build/build_config.h"
 #include "ui/accessibility/ax_enums.h"
 #include "ui/base/accelerators/accelerator.h"
+#include "ui/base/class_property.h"
 #include "ui/base/dragdrop/drag_drop_types.h"
 #include "ui/base/dragdrop/drop_target_event.h"
 #include "ui/base/dragdrop/os_exchange_data.h"
@@ -115,7 +116,8 @@ class VIEWS_EXPORT View : public ui::LayerDelegate,
                           public ui::LayerOwner,
                           public ui::AcceleratorTarget,
                           public ui::EventTarget,
-                          public ui::EventHandler {
+                          public ui::EventHandler,
+                          public ui::PropertyHandler {
  public:
   using Views = std::vector<View*>;