Fixed position of plus image on action box button; added ICON_CENTERED placement to TextButton

ui/views/controls/button/text_button.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_CONTROLS_BUTTON_TEXT_BUTTON_H_
 #define UI_VIEWS_CONTROLS_BUTTON_TEXT_BUTTON_H_
 
 #include <string>
 
 #include "base/compiler_specific.h"
@@ skipping 310 matching lines @@
   // Sets the icon.
   virtual void SetIcon(const gfx::ImageSkia& icon);
   virtual void SetHoverIcon(const gfx::ImageSkia& icon);
   virtual void SetPushedIcon(const gfx::ImageSkia& icon);
 
   bool HasIcon() const { return !icon_.isNull(); }
 
   // Meanings are reversed for right-to-left layouts.
   enum IconPlacement {
     ICON_ON_LEFT,
-    ICON_ON_RIGHT
+    ICON_ON_RIGHT,
+    ICON_CENTERED  // Centered is valid only when text is empty.
   };
 
   IconPlacement icon_placement() { return icon_placement_; }
   void set_icon_placement(IconPlacement icon_placement) {
+    // ICON_CENTERED works only when |text_| is empty.
+    DCHECK((icon_placement != ICON_CENTERED) || text_.empty());
     icon_placement_ = icon_placement;
   }
 
   void set_ignore_minimum_size(bool ignore_minimum_size);
 
   // Overridden from View:
   virtual gfx::Size GetPreferredSize() OVERRIDE;
   virtual std::string GetClassName() const OVERRIDE;
   virtual void OnPaintFocusBorder(gfx::Canvas* canvas) OVERRIDE;
 
@@ skipping 67 matching lines @@
   // Overridden from TextButton:
   virtual void GetExtraParams(
       ui::NativeTheme::ExtraParams* params) const OVERRIDE;
 
   DISALLOW_COPY_AND_ASSIGN(NativeTextButton);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_BUTTON_TEXT_BUTTON_H_