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.
  *
  * 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
@@ skipping 247 matching lines @@
         void clipOutRoundedRect(const RoundedRect&);
         void clipPath(const Path&, WindRule);
         void clipConvexPolygon(size_t numPoints, const FloatPoint*, bool antialias = true);
         void clipToImageBuffer(ImageBuffer*, const FloatRect&);
         
         IntRect clipBounds() const;
 
         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 TextRun&, const FloatPoint&, const FloatRect& textRect, int from = 0, int to = -1);
+        void drawEmphasisMarks(const Font&, const TextRun& , const AtomicString& mark, const FloatPoint&, const FloatRect& textRect, int from = 0, int to = -1);
+        void drawBidiText(const Font&, const TextRun&, const FloatPoint&, const FloatRect& textRect, 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 155 matching lines @@
 
     private:
         GraphicsContext& m_context;
         bool m_saveAndRestore;
     };
 
 } // namespace WebCore
 
 #endif // GraphicsContext_h