linux_aura: Make X11 selection buffers work on text in both direction.

ui/base/clipboard/clipboard.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_BASE_CLIPBOARD_CLIPBOARD_H_
 #define UI_BASE_CLIPBOARD_CLIPBOARD_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 160 matching lines @@
   // buffer.
   enum Buffer {
     BUFFER_STANDARD,
     BUFFER_SELECTION,
   };
 
   static bool IsValidBuffer(int32 buffer) {
     switch (buffer) {
       case BUFFER_STANDARD:
         return true;
-#if defined(USE_X11) && !defined(USE_AURA)
+#if defined(USE_X11) && !defined(OS_CHROMEOS)
       case BUFFER_SELECTION:
         return true;
 #endif
     }
     return false;
   }
 
   static Buffer FromInt(int32 buffer) {
     return static_cast<Buffer>(buffer);
   }
@@ skipping 197 matching lines @@
   class AuraX11Details;
   scoped_ptr<AuraX11Details> aurax11_details_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(Clipboard);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_CLIPBOARD_CLIPBOARD_H_