Track the region where text is painted.

Source/WebKit/chromium/src/WebFontImpl.cpp

 /*
  * Copyright (C) 2010 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 84 matching lines @@
 {
     FontCachePurgePreventer fontCachePurgePreventer;
 
     GraphicsContextBuilder builder(canvas);
     GraphicsContext& gc = builder.context();
 
     gc.save();
     gc.setShouldSmoothFonts(canvasIsOpaque);
     gc.setFillColor(color, ColorSpaceDeviceRGB);
     gc.clip(WebCore::FloatRect(clip));
-    m_font.drawText(&gc, run, leftBaseline, from, to);
+    m_font.drawText(&gc, run, leftBaseline, WebCore::FloatRect(clip), from, to);

[eseidel, 2013/04/18 21:04:38]

nit: Seems like a local would be useful.  We do this FloatRect convert twice.

[alokp, 2013/04/18 22:22:37]

Done.

     gc.restore();
 
 #if defined(WIN32)
     if (canvasIsOpaque && SkColorGetA(color) == 0xFF && !canvas->isDrawingToLayer()) {
         // The text drawing logic on Windows ignores the alpha component
         // intentionally, for performance reasons.
         // (Please see TransparencyAwareFontPainter::initializeForGDI in
         // FontChromiumWin.cpp.)
         const SkBitmap& bitmap = canvas->getTopDevice()->accessBitmap(true);
         IntRect textBounds = estimateTextBounds(run, leftBaseline);
@@ skipping 31 matching lines @@
     FontCachePurgePreventer fontCachePurgePreventer;
     int totalWidth = m_font.width(run, 0);
     const WebCore::FontMetrics& fontMetrics = m_font.fontMetrics();
     return WebRect(leftBaseline.x - (fontMetrics.ascent() + fontMetrics.descent()) / 2,
                    leftBaseline.y - fontMetrics.ascent() - fontMetrics.lineGap(),
                    totalWidth + fontMetrics.ascent() + fontMetrics.descent(),
                    fontMetrics.lineSpacing()); 
 }
 
 } // namespace WebKit