Track the region where text is painted.

Source/core/html/canvas/CanvasRenderingContext2D.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  * Copyright (C) 2012 Intel Corporation. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
@@ skipping 2183 matching lines @@
                                    width + fontMetrics.height(), fontMetrics.lineSpacing());
     if (!fill)
         inflateStrokeRect(textRect);
 
     c->setTextDrawingMode(fill ? TextModeFill : TextModeStroke);
     if (useMaxWidth) {
         GraphicsContextStateSaver stateSaver(*c);
         c->translate(location.x(), location.y());
         // We draw when fontWidth is 0 so compositing operations (eg, a "copy" op) still work.
         c->scale(FloatSize((fontWidth > 0 ? (width / fontWidth) : 0), 1));
-        c->drawBidiText(font, textRun, FloatPoint(0, 0), Font::UseFallbackIfFontNotReady);
+        c->drawBidiText(font, textRun, FloatPoint(0, 0), textRect, Font::UseFallbackIfFontNotReady);
     } else
-        c->drawBidiText(font, textRun, location, Font::UseFallbackIfFontNotReady);
+        c->drawBidiText(font, textRun, location, textRect, Font::UseFallbackIfFontNotReady);
 
     didDraw(textRect);
 }
 
 void CanvasRenderingContext2D::inflateStrokeRect(FloatRect& rect) const
 {
     // Fast approximation of the stroke's bounding rect.
     // This yields a slightly oversized rect but is very fast
     // compared to Path::strokeBoundingRect().
     static const float root2 = sqrtf(2);
@@ skipping 31 matching lines @@
         return;
 
     realizeSaves();
     modifiableState().m_imageSmoothingEnabled = enabled;
     GraphicsContext* c = drawingContext();
     if (c)
         c->setImageInterpolationQuality(enabled ? DefaultInterpolationQuality : InterpolationNone);
 }
 
 } // namespace WebCore