Introduce use counters for shadow DOM handling in plainText()

Source/core/editing/FindOptions.h

 /*
  * Copyright (C) 2010 Apple 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 19 matching lines @@
 
 enum FindOptionFlag {
     CaseInsensitive = 1 << 0,
     AtWordStarts = 1 << 1,
     // When combined with AtWordStarts, accepts a match in the middle of a word if the match begins with
     // an uppercase letter followed by a lowercase or non-letter. Accepts several other intra-word matches.
     TreatMedialCapitalAsWordStart = 1 << 2,
     Backwards = 1 << 3,
     WrapAround = 1 << 4,
     StartInSelection = 1 << 5,
-    WholeWord = 1 << 6 // WholeWord should imply AtWordStarts
+    WholeWord = 1 << 6, // WholeWord should imply AtWordStarts
+    // TODO(yosin) Once find UI works on composed tree and it doesn't use
+    // |rangeOfString()|, we should get rid of |FindAPICall| enum member.
+    FindAPICall = 1 << 7, // Used for Window.find or execCommand('find')
 };
 
 typedef unsigned FindOptions;
 
 } // namespace blink
 
 #endif // FindOptions_h