Change Font::offsetForPositionForComplexText to use CachingWordShapeIterator

Source/platform/fonts/shaping/CachingWordShaper.h

 /*
  * Copyright (C) 2015 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.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 31 matching lines @@
 
 class PLATFORM_EXPORT CachingWordShaper final {
 public:
     CachingWordShaper();
     ~CachingWordShaper();
     void clear();
 
     float width(const Font*, const TextRun&,
         HashSet<const SimpleFontData*>* fallbackFonts,
         FloatRect* glyphBounds);
+    int offsetForPosition(const Font*, const TextRun&, float targetX);
     float fillGlyphBuffer(const Font*, const TextRun&,
         HashSet<const SimpleFontData*>*, GlyphBuffer*,
         unsigned from, unsigned to);
     float fillGlyphBufferForTextEmphasis(const Font*, const TextRun&,
         const GlyphData* emphasisData, GlyphBuffer*,
         unsigned from, unsigned to);
     FloatRect selectionRect(const Font*, const TextRun&, const FloatPoint&,
         int height, unsigned from, unsigned to);
 
 private:
     OwnPtr<ShapeCache> m_shapeCache;
 };
 
 } // namespace blink
 
 #endif // CachingWordShaper_h