Get rid of redundant using statements in VisibleUnit.cpp

Source/core/editing/VisibleUnits.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 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 45 matching lines @@
 #include "core/layout/line/InlineIterator.h"
 #include "core/layout/line/InlineTextBox.h"
 #include "core/paint/DeprecatedPaintLayer.h"
 #include "platform/Logging.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/heap/Handle.h"
 #include "platform/text/TextBoundaries.h"
 
 namespace blink {
 
-using namespace HTMLNames;
-using namespace WTF::Unicode;
-
 template <typename PositionType>
 static PositionType canonicalizeCandidate(const PositionType& candidate)
 {
     if (candidate.isNull())
         return PositionType();
     ASSERT(isVisuallyEquivalentCandidate(candidate));
     PositionType upstream = mostBackwardCaretPosition(candidate);
     if (isVisuallyEquivalentCandidate(upstream))
         return upstream;
     return candidate;
@@ skipping 2889 matching lines @@
         return honorEditingBoundaryAtOrBefore(prev, visiblePosition.deepEquivalent());
     case CanSkipOverEditingBoundary:
         return skipToStartOfEditingBoundary(prev, visiblePosition.deepEquivalent());
     }
 
     ASSERT_NOT_REACHED();
     return honorEditingBoundaryAtOrBefore(prev, visiblePosition.deepEquivalent());
 }
 
 } // namespace blink