Make VisibleSelection::AppendTrailingWhitespace() as const function

third_party/WebKit/Source/core/editing/VisibleSelection.h

 /*
  * Copyright (C) 2004 Apple Computer, 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.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 93 matching lines @@
     return IsRange() && !Start().IsOrphan() && !End().IsOrphan();
   }
   bool IsNonOrphanedCaretOrRange() const {
     return !IsNone() && !Start().IsOrphan() && !End().IsOrphan();
   }
 
   // True if base() <= extent().
   bool IsBaseFirst() const { return base_is_first_; }
   bool IsDirectional() const { return is_directional_; }
 
-  void AppendTrailingWhitespace();
+  VisibleSelectionTemplate<Strategy> AppendTrailingWhitespace() const;
 
   // TODO(yosin) Most callers probably don't want these functions, but
   // are using them for historical reasons. |toNormalizedEphemeralRange()|
   // contracts the range around text, and moves the caret most backward
   // visually equivalent position before returning the range/positions.
   EphemeralRangeTemplate<Strategy> ToNormalizedEphemeralRange() const;
 
   Element* RootEditableElement() const;
   bool IsContentEditable() const;
   bool HasEditableStyle() const;
@@ skipping 85 matching lines @@
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showTree(const blink::VisibleSelection&);
 void showTree(const blink::VisibleSelection*);
 void showTree(const blink::VisibleSelectionInFlatTree&);
 void showTree(const blink::VisibleSelectionInFlatTree*);
 #endif
 
 #endif  // VisibleSelection_h