BoxLayout now suports per-view margins.

ui/views/view_properties.cc

Index: ui/views/view_properties.cc
diff --git a/ui/views/view_properties.cc b/ui/views/view_properties.cc
new file mode 100644
index 0000000000000000000000000000000000000000..3f5d1c3539ad18afc1883f9742e6ca3d0ae11fa5
--- /dev/null
+++ b/ui/views/view_properties.cc
@@ -0,0 +1,15 @@
+// Copyright 2017 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.
+
+#include "ui/views/view_properties.h"
+
+#include "ui/gfx/geometry/insets.h"
+
+DECLARE_EXPORTED_UI_CLASS_PROPERTY_TYPE(VIEWS_EXPORT, gfx::Insets*);
+
+namespace views {
+
+DEFINE_OWNED_UI_CLASS_PROPERTY_KEY(gfx::Insets, kMarginsKey, nullptr);
+
+}  // namespace views