Move DOMSelection.[cpp/h] from core/page to core/editing

Source/core/editing/Selection.idl

 /*
  * Copyright (C) 2007 Apple Inc.  All rights reserved.
  * Copyright (C) 2009 Google Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 76 matching lines @@
                                                                                  [Default=Undefined] optional long baseOffset,
                                                                                  [Default=Undefined] optional Node extentNode,
                                                                                  [Default=Undefined] optional long extentOffset);
     [ImplementedAs=collapse, MeasureAs=SelectionSetPosition, RaisesException, TypeChecking=Interface] void setPosition(Node node,
                                                                                                                        optional long offset);
 
     // IE extensions
     // http://msdn.microsoft.com/en-us/library/ms535869(VS.85).aspx
     [MeasureAs=SelectionEmpty] void empty();
 };