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 d1f69707fda4a74ca022439077464b8205df2fb0..9a409446ead656ed6855c7335ec5f7b8e1cca4e2 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*>;
 
@@ -1697,6 +1699,11 @@ class VIEWS_EXPORT View : public ui::LayerDelegate,
   DISALLOW_COPY_AND_ASSIGN(View);
 };
 
+// A property to store margins around the outer perimeter of the view. Margins
+// are outside the bounds of the view. This is used by various layout managers
+// to position views with the proper spacing between them.
+VIEWS_EXPORT extern const ui::ClassProperty<gfx::Insets*>* const kMarginsKey;
+
 }  // namespace views
 
 #endif  // UI_VIEWS_VIEW_H_