Switch tab.cc to use an empty border for the contents.

ui/views/border.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_BORDER_H_
 #define UI_VIEWS_BORDER_H_
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "third_party/skia/include/core/SkColor.h"
@@ skipping 33 matching lines @@
 
   // Convenience for creating a scoped_ptr with no Border.
   static scoped_ptr<Border> NullBorder();
 
   // Creates a border that is a simple line of the specified thickness and
   // color.
   static scoped_ptr<Border> CreateSolidBorder(int thickness, SkColor color);
 
   // Creates a border for reserving space. The returned border does not
   // paint anything.
+  static scoped_ptr<Border> CreateEmptyBorder(const gfx::Insets& insets);
   static scoped_ptr<Border> CreateEmptyBorder(int top,
                                               int left,
                                               int bottom,
                                               int right);
 
   // Creates a border of the specified color, and specified thickness on each
   // side.
   static scoped_ptr<Border> CreateSolidSidedBorder(int top,
                                                    int left,
                                                    int bottom,
@@ skipping 20 matching lines @@
   // content laid out relative to these images.
   virtual gfx::Size GetMinimumSize() const = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(Border);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_BORDER_H_