Enable srcset support in HTMLImageElement

Source/core/html/HTMLImageElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 #include "config.h"
 #include "core/html/HTMLImageElement.h"
 
 #include "CSSPropertyNames.h"
 #include "HTMLNames.h"
+#include "RuntimeEnabledFeatures.h"
 #include "bindings/v8/ScriptEventListener.h"
 #include "core/dom/Attribute.h"
 #include "core/dom/EventNames.h"
 #include "core/fetch/ImageResource.h"
 #include "core/html/HTMLAnchorElement.h"
 #include "core/html/HTMLFormElement.h"
 #include "core/html/parser/HTMLParserIdioms.h"
 #include "core/rendering/RenderImage.h"
 
 using namespace std;
@@ skipping 62 matching lines @@
         addHTMLLengthToStyle(style, CSSPropertyMarginLeft, value);
         addHTMLLengthToStyle(style, CSSPropertyMarginRight, value);
     } else if (name == alignAttr)
         applyAlignmentAttributeToStyle(value, style);
     else if (name == valignAttr)
         addPropertyToPresentationAttributeStyle(style, CSSPropertyVerticalAlign, value);
     else
         HTMLElement::collectStyleForPresentationAttribute(name, value, style);
 }
 
+const AtomicString HTMLImageElement::imageSourceURL() const
+{
+    return m_bestFitImageURL.isEmpty() ? fastGetAttribute(srcAttr) : m_bestFitImageURL;

[do-not-use, 2013/09/12 08:23:53]

Wouldn't isNull() suffice? Can bestFitSourceForImageAttributes() really return
an empty string?

[Yoav Weiss, 2013/09/12 09:30:20]

m_bestFitImageURL is initialized as an empty string, and
bestFitSourceImageAttributes() can return an empty string, if both srcSttr and
srcsetAttr's values are empty (or srcsetAttr's value is invalid).

Both can be modified to a null string, which will enable an isNull check here.
What are the benefits? Is isNull() faster than isEmpty()?

[do-not-use, 2013/09/12 09:56:37]

To be clear the default constructor for String creates a NULL string, not an
empty one. Unless I am mistaken, m_bestFitImageURL is initially a NULL string
and bestFitSourceImageAttributes() may return String(), which is a NULL string
as well.

To answer your question, yes, isNull() is faster than isEmpty() still isEmpty()
checks if the string is null or empty (2 checks instead of 1).

+}
+
 void HTMLImageElement::parseAttribute(const QualifiedName& name, const AtomicString& value)
 {
     if (name == altAttr) {
         if (renderer() && renderer()->isImage())
             toRenderImage(renderer())->updateAltText();
-    } else if (name == srcAttr)
+    } else if (name == srcAttr || name == srcsetAttr) {
+        if (RuntimeEnabledFeatures::srcsetEnabled())
+            m_bestFitImageURL = bestFitSourceForImageAttributes(document().devicePixelRatio(), fastGetAttribute(srcAttr), fastGetAttribute(srcsetAttr));
         m_imageLoader.updateFromElementIgnoringPreviousError();
+    }
     else if (name == usemapAttr)
         setIsLink(!value.isNull());
     else if (name == onbeforeloadAttr)
         setAttributeEventListener(eventNames().beforeloadEvent, createAttributeEventListener(this, name, value));
     else if (name == compositeAttr) {
         // FIXME: images don't support blend modes in their compositing attribute.
         BlendMode blendOp = BlendModeNormal;
         if (!parseCompositeAndBlendOperator(value, m_compositeOperator, blendOp))
             m_compositeOperator = CompositeSourceOver;
     } else
@@ skipping 240 matching lines @@
 
 Image* HTMLImageElement::imageContents()
 {
     if (!m_imageLoader.imageComplete())
         return 0;
 
     return m_imageLoader.image()->image();
 }
 
 }