Add preloader support for picture based source selection

Source/core/html/parser/HTMLPreloadScanner.h

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * 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:
  * 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 56 matching lines @@
 private:
     class StartTagScanner;
 
     template<typename Token>
     inline void scanCommon(const Token&, const SegmentedString&, PreloadRequestStream& requests);
 
     template<typename Token>
     void updatePredictedBaseURL(const Token&);
 
     struct Checkpoint {
-        Checkpoint(const KURL& predictedBaseElementURL, bool inStyle, size_t templateCount)
+        Checkpoint(const KURL& predictedBaseElementURL, bool inStyle, const Vector<String>& pictureSourceURLStack, size_t templateCount)
             : predictedBaseElementURL(predictedBaseElementURL)
             , inStyle(inStyle)
+            , pictureSourceURLStack(pictureSourceURLStack)

[eseidel, 2014/05/09 07:30:36]

Why do these need to be stored on the checkpoint?  I guess this is part of the
fake-tree-builder state?

             , templateCount(templateCount)
         {
         }
 
         KURL predictedBaseElementURL;
         bool inStyle;
+        Vector<String> pictureSourceURLStack;
         size_t templateCount;
     };
 
     CSSPreloadScanner m_cssScanner;
     const KURL m_documentURL;
     KURL m_predictedBaseElementURL;
     bool m_inStyle;
+    Vector<String> m_pictureSourceURLStack;
     size_t m_templateCount;
     RefPtr<MediaValues> m_mediaValues;
 
     Vector<Checkpoint> m_checkpoints;
 };
 
 class HTMLPreloadScanner {
     WTF_MAKE_NONCOPYABLE(HTMLPreloadScanner); WTF_MAKE_FAST_ALLOCATED;
 public:
     HTMLPreloadScanner(const HTMLParserOptions&, const KURL& documentURL, PassRefPtr<MediaValues>);
     ~HTMLPreloadScanner();
 
     void appendToEnd(const SegmentedString&);
     void scan(HTMLResourcePreloader*, const KURL& documentBaseElementURL);
 
 private:
     TokenPreloadScanner m_scanner;
     SegmentedString m_source;
     HTMLToken m_token;
     OwnPtr<HTMLTokenizer> m_tokenizer;
 };
 
 }
 
 #endif