Draw a single underline for text-decoration-style: [dashed, dotted].

Source/core/rendering/InlineTextBox.cpp

 /*
  * (C) 1999 Lars Knoll (knoll@kde.org)
  * (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 1074 matching lines @@
     // Using computedFontSize should take care of zoom as well.
 
     // Update Underline thickness, in case we have Faulty Font Metrics calculating underline thickness by old method.
     float textDecorationThickness = styleToUse->fontMetrics().underlineThickness();
     int fontHeightInt  = (int)(styleToUse->fontMetrics().floatHeight() + 0.5);
     if ((textDecorationThickness == 0.f) || (textDecorationThickness >= (fontHeightInt >> 1)))
         textDecorationThickness = std::max(1.f, styleToUse->computedFontSize() / 10.f);
 
     context->setStrokeThickness(textDecorationThickness);
 
+    switch (decorationStyle) {
+    case TextDecorationStyleSolid:
+    case TextDecorationStyleDouble:
+    case TextDecorationStyleDotted:
+    case TextDecorationStyleDashed:
+        context->setShouldAntialias(RenderBoxModelObject::shouldAntialiasLines(context));
+        break;
+    }
+
     float extraOffset = 0;
     if (!linesAreOpaque && shadowCount > 1) {
         FloatRect clipRect(localOrigin, FloatSize(width, baseline + 2));
         for (size_t i = shadowCount; i--; ) {
             const ShadowData& s = shadowList->shadows()[i];
             FloatRect shadowRect(localOrigin, FloatSize(width, baseline + 2));
             shadowRect.inflate(s.blur());
             float shadowX = isHorizontal() ? s.x() : s.y();
             float shadowY = isHorizontal() ? s.y() : -s.x();
             shadowRect.move(shadowX, shadowY);
@@ skipping 449 matching lines @@
     printedCharacters = fprintf(stderr, "\t%s %p", obj.renderName(), &obj);
     const int rendererCharacterOffset = 24;
     for (; printedCharacters < rendererCharacterOffset; printedCharacters++)
         fputc(' ', stderr);
     fprintf(stderr, "(%d,%d) \"%s\"\n", start(), start() + len(), value.utf8().data());
 }
 
 #endif
 
 } // namespace WebCore