Add preloader support for picture based source selection

Source/core/html/parser/HTMLPreloadScanner.h

Index: Source/core/html/parser/HTMLPreloadScanner.h
diff --git a/Source/core/html/parser/HTMLPreloadScanner.h b/Source/core/html/parser/HTMLPreloadScanner.h
index 8117458c98585c4aa48e371e5603d1393ee35c91..6a7f99d7c3ef7630f14d14b2e88d53bd615fc101 100644
--- a/Source/core/html/parser/HTMLPreloadScanner.h
+++ b/Source/core/html/parser/HTMLPreloadScanner.h
@@ -86,10 +86,20 @@ private:
         size_t templateCount;
     };
 
+    struct Parent {
+        String sourceURL;
+        const StringImpl* tagImpl;
+        Parent(const StringImpl* tagImpl)
+            : tagImpl(tagImpl)
+        {
+        }
+    };
+
     CSSPreloadScanner m_cssScanner;
     const KURL m_documentURL;
     KURL m_predictedBaseElementURL;
     bool m_inStyle;
+    Vector<Parent> m_pictureParentStack;
     size_t m_templateCount;
     RefPtr<MediaValues> m_mediaValues;