Introduce firstRangeOf() as replacement of VisibleSelection::firstRange()

Source/web/TextFinder.cpp

 /*
  * 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 116 matching lines @@
 
     if (m_activeMatch && &m_activeMatch->ownerDocument() != ownerFrame().frame()->document())
         m_activeMatch = nullptr;
 
     // If the user has selected something since the last Find operation we want
     // to start from there. Otherwise, we start searching from where the last Find
     // operation left off (either a Find or a FindNext operation).
     VisibleSelection selection(ownerFrame().frame()->selection().selection());
     bool activeSelection = !selection.isNone();
     if (activeSelection) {
-        m_activeMatch = selection.firstRange().get();
+        m_activeMatch = firstRangeOf(selection).get();
         ownerFrame().frame()->selection().clear();
     }
 
     ASSERT(ownerFrame().frame() && ownerFrame().frame()->view());
     const FindOptions findOptions = (options.forward ? 0 : Backwards)
         | (options.matchCase ? 0 : CaseInsensitive)
         | (wrapWithinFrame ? WrapAround : 0)
         | (options.wordStart ? AtWordStarts : 0)
         | (options.medialCapitalAsWordStart ? TreatMedialCapitalAsWordStart : 0)
         | (options.findNext ? 0 : StartInSelection);
@@ skipping 654 matching lines @@
     visitor->trace(m_ownerFrame);
     visitor->trace(m_currentActiveMatchFrame);
     visitor->trace(m_activeMatch);
     visitor->trace(m_resumeScopingFromRange);
     visitor->trace(m_deferredScopingWork);
     visitor->trace(m_findMatchesCache);
 #endif
 }
 
 } // namespace blink