HTMLPreloadScanner should only use valid <base> urls

Source/core/html/parser/HTMLPreloadScanner.cpp

Index: Source/core/html/parser/HTMLPreloadScanner.cpp
diff --git a/Source/core/html/parser/HTMLPreloadScanner.cpp b/Source/core/html/parser/HTMLPreloadScanner.cpp
index a98df60e30f99459ef336dd255f28deb2d1f4c31..d554c9b3c8c7a38a717b2e59b88254e44d473d9e 100644
--- a/Source/core/html/parser/HTMLPreloadScanner.cpp
+++ b/Source/core/html/parser/HTMLPreloadScanner.cpp
@@ -515,8 +515,10 @@ template<typename Token>
 void TokenPreloadScanner::updatePredictedBaseURL(const Token& token)
 {
     ASSERT(m_predictedBaseElementURL.isEmpty());
-    if (const typename Token::Attribute* hrefAttribute = token.getAttributeItem(hrefAttr))
-        m_predictedBaseElementURL = KURL(m_documentURL, stripLeadingAndTrailingHTMLSpaces(hrefAttribute->value)).copy();
+    if (const typename Token::Attribute* hrefAttribute = token.getAttributeItem(hrefAttr)) {
+        KURL url(m_documentURL, stripLeadingAndTrailingHTMLSpaces(hrefAttribute->value));
+        m_predictedBaseElementURL = url.isValid() ? url.copy() : KURL();
+    }
 }
 
 HTMLPreloadScanner::HTMLPreloadScanner(const HTMLParserOptions& options, const KURL& documentURL, PassRefPtr<MediaValues> mediaValues)