Fix Harmony popover buttons being flush with their content.

ui/views/layout/layout_provider.h

 // 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.
 
 #ifndef UI_VIEWS_LAYOUT_LAYOUT_PROVIDER_H_
 #define UI_VIEWS_LAYOUT_LAYOUT_PROVIDER_H_
 
 #include "base/macros.h"
 #include "ui/gfx/geometry/insets.h"
 #include "ui/views/style/typography_provider.h"
@@ skipping 31 matching lines @@
   // All Insets enum values must be below this value.
   VIEWS_INSETS_MAX = 0x1000
 };
 
 enum DistanceMetric {
   // DistanceMetric enum values must always be greater than any InsetsMetric
   // value. This allows the code to verify at runtime that arguments of the
   // two types have not been interchanged.
   VIEWS_DISTANCE_START = VIEWS_INSETS_MAX,
 
+  // If a bubble has buttons, this is the margin between them and the rest of
+  // the content.
+  DISTANCE_BUBBLE_BUTTON_TOP_MARGIN = VIEWS_DISTANCE_START,
   // Margin on the left and right of the contents of a bubble.
-  DISTANCE_BUBBLE_CONTENTS_HORIZONTAL_MARGIN = VIEWS_DISTANCE_START,
+  DISTANCE_BUBBLE_CONTENTS_HORIZONTAL_MARGIN,
   // Margin on the top and bottom of the contents of a bubble.
   DISTANCE_BUBBLE_CONTENTS_VERTICAL_MARGIN,
   // The default padding to add on each side of a button's label.
   DISTANCE_BUTTON_HORIZONTAL_PADDING,
   // The maximum width a button can have and still influence the sizes of
   // other linked buttons.  This allows short buttons to have linked widths
   // without long buttons making things overly wide.
   DISTANCE_BUTTON_MAX_LINKABLE_WIDTH,
   // The distance between a dialog's edge and the close button in the upper
   // trailing corner.
@@ skipping 46 matching lines @@
 
  private:
   DefaultTypographyProvider typography_provider_;
 
   DISALLOW_COPY_AND_ASSIGN(LayoutProvider);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_LAYOUT_LAYOUT_PROVIDER_H_