BoxLayout now suports per-view margins.

ui/views/view.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_VIEWS_VIEW_H_
 #define UI_VIEWS_VIEW_H_
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <map>
 #include <memory>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/compiler_specific.h"
 #include "base/i18n/rtl.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #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"
 #include "ui/base/ui_base_types.h"
 #include "ui/compositor/layer_delegate.h"
 #include "ui/compositor/layer_owner.h"
 #include "ui/compositor/paint_cache.h"
 #include "ui/events/event.h"
 #include "ui/events/event_target.h"
 #include "ui/gfx/geometry/insets.h"
@@ skipping 74 matching lines @@
 //   specific properties and functionality.
 //
 //   Unless otherwise documented, views is not thread safe and should only be
 //   accessed from the main thread.
 //
 /////////////////////////////////////////////////////////////////////////////
 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*>;
 
   enum class FocusBehavior {
     // Use when the View is never focusable. Default.
     NEVER,
 
     // Use when the View is to be focusable both in regular and accessibility
     // mode.
     ALWAYS,
@@ skipping 1561 matching lines @@
   // The accessibility element used to represent this View.
   std::unique_ptr<NativeViewAccessibility> native_view_accessibility_;
 
   // Observers -------------------------------------------------------------
 
   base::ObserverList<ViewObserver> observers_;
 
   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;

[sky, 2017/05/15 20:29:10]

Please move this into a separate file (I commented on this in an earlier patch
with recommendations as to where to put it).

[kylix_rd, 2017/05/16 18:45:48]

Oops. My bad. I completely missed that comment.

+
 }  // namespace views
 
 #endif  // UI_VIEWS_VIEW_H_