Add ability to specify extra insets for a view via its border.

ui/views/border.h

Index: ui/views/border.h
diff --git a/ui/views/border.h b/ui/views/border.h
index d30cc7ca0b00e2882b2b5288d9b058a98fa3858d..5a7b8c34d3bfa1872f107c32ab51969bb7a6e922 100644
--- a/ui/views/border.h
+++ b/ui/views/border.h
@@ -73,6 +73,19 @@ class VIEWS_EXPORT Border {
                                                         int right,
                                                         SkColor color);
 
+  // Adds extra, unpainted insets to |border|. This is effectively equivalent to
+  // adding an EmptyBorder and then |border|. Example:

[sky, 2016/11/04 15:32:53]

optional:
I would take this second sentence to mean |border| is painted on the inside of
the EmptyBorder, which isn't quite what is happening. Maybe something like:

Creates a new border that draws |border| and adds additional padding. This is
equivalent to changing the insets of |border| without changing how or what it
paints.

I favor a name of WrapBorderWithPadding, but I realize naming is hard and leave
it to you. I would actually prefer Create in the name, but it's hard to get
something that sounds reasonable.

[Evan Stade, 2016/11/04 15:50:16]

ok
CreatePaddedBorder?

while we're at it, how can we make this less verbose:

  views::Border::CreateRoundedRectBorder

Options that come to mind:

a) views::CreateRoundedRectBorder (promote to standalone static fn in views
namespace)
b) views::Border::CreateRoundedRect (remove trailing "Border")

+  //
+  // view->SetBorder(Border::AddInteriorPadding(
+  //                     Border::CreateSolidBorder(1, SK_ColorRED),
+  //                     gfx::Insets(2, 0, 0, 0)));
+  //
+  // yields a single dip red border and an additional 2dip of unpainted padding
+  // above the view content (below the border).
+  static std::unique_ptr<Border> AddInteriorPadding(
+      std::unique_ptr<Border> border,
+      const gfx::Insets& insets);
+
   // Creates a Border from the specified Painter.
   // |insets| define size of an area allocated for a Border.
   static std::unique_ptr<Border> CreateBorderPainter(