Track the region where text is painted.

Source/core/platform/graphics/GraphicsContext.h

 /*
  * Copyright (C) 2003, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2008-2009 Torch Mobile, Inc.
  * Copyright (C) 2013 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.
@@ skipping 51 matching lines @@
 
     class AffineTransform;
     class DrawingBuffer;
     class Generator;
     class ImageBuffer;
     class IntRect;
     class RoundedRect;
     class KURL;
     class GraphicsContext3D;
     class TextRun;
+    struct TextRunPaintInfo;
     class TransformationMatrix;
 
     enum TextDrawingMode {
         TextModeFill      = 1 << 0,
         TextModeStroke    = 1 << 1,
     };
     typedef unsigned TextDrawingModeFlags;
 
     enum StrokeStyle {
         NoStroke,
@@ skipping 183 matching lines @@
         void clipRoundedRect(const RoundedRect&);
         void clipOut(const IntRect&);
         void clipOutRoundedRect(const RoundedRect&);
         void clipPath(const Path&, WindRule);
         void clipConvexPolygon(size_t numPoints, const FloatPoint*, bool antialias = true);
         void clipToImageBuffer(ImageBuffer*, const FloatRect&);
         
         TextDrawingModeFlags textDrawingMode() const;
         void setTextDrawingMode(TextDrawingModeFlags);
 
-        void drawText(const Font&, const TextRun&, const FloatPoint&, int from = 0, int to = -1);
-        void drawEmphasisMarks(const Font&, const TextRun& , const AtomicString& mark, const FloatPoint&, int from = 0, int to = -1);
-        void drawBidiText(const Font&, const TextRun&, const FloatPoint&, Font::CustomFontNotReadyAction = Font::DoNotPaintIfFontNotReady);
+        void drawText(const Font&, const TextRunPaintInfo&, const FloatPoint&);
+        void drawEmphasisMarks(const Font&, const TextRunPaintInfo&, const AtomicString& mark, const FloatPoint&);
+        void drawBidiText(const Font&, const TextRunPaintInfo&, const FloatPoint&, Font::CustomFontNotReadyAction = Font::DoNotPaintIfFontNotReady);
         void drawHighlightForText(const Font&, const TextRun&, const FloatPoint&, int h, const Color& backgroundColor, ColorSpace, int from = 0, int to = -1);
 
         enum RoundingMode {
             RoundAllSides,
             RoundOriginAndDimensions
         };
         FloatRect roundToDevicePixels(const FloatRect&, RoundingMode = RoundAllSides);
 
         void drawLineForText(const FloatPoint&, float width, bool printing);
         enum DocumentMarkerLineStyle {
@@ skipping 149 matching lines @@
 
     private:
         GraphicsContext& m_context;
         bool m_saveAndRestore;
     };
 
 } // namespace WebCore
 
 #endif // GraphicsContext_h