Add the button style for combobox

ui/views/controls/button/menu_button.cc

 // 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.
 
 #include "ui/views/controls/button/menu_button.h"
 
 #include "base/strings/utf_string_conversions.h"
 #include "grit/ui_resources.h"
 #include "grit/ui_strings.h"
 #include "ui/base/accessibility/accessible_view_state.h"
@@ skipping 131 matching lines @@
 
 ////////////////////////////////////////////////////////////////////////////////
 //
 // MenuButton - Events
 //
 ////////////////////////////////////////////////////////////////////////////////
 
 gfx::Size MenuButton::GetPreferredSize() {
   gfx::Size prefsize = TextButton::GetPreferredSize();
   if (show_menu_marker_) {
-    prefsize.Enlarge(menu_marker_->width() + kMenuMarkerPaddingLeft +
-                         kMenuMarkerPaddingRight,
-                     0);
+    int width = menu_marker_->width() + kMenuMarkerPaddingRight;
+    if (!text().empty())
+      width += kMenuMarkerPaddingLeft;
+    prefsize.Enlarge(width, 0);
   }
   return prefsize;
 }
 
 const char* MenuButton::GetClassName() const {
   return kViewClassName;
 }
 
 bool MenuButton::OnMousePressed(const ui::MouseEvent& event) {
   RequestFocus();
@@ skipping 106 matching lines @@
   if (!GetWidget()) {
     NOTREACHED();
     return 0;
   }
 
   gfx::Rect monitor_bounds = GetWidget()->GetWorkAreaBoundsInScreen();
   return monitor_bounds.right() - 1;
 }
 
 }  // namespace views