Use SizesAttributeParser to get the right srcset resource

Source/core/css/parser/MediaQueryTokenizer.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/css/parser/MediaQueryTokenizer.h"
 
 namespace WebCore {
 #include "MediaQueryTokenizerCodepoints.cpp"
 }
@@ skipping 195 matching lines @@
 void MediaQueryTokenizer::tokenize(String string, Vector<MediaQueryToken>& outTokens)
 {
     // According to the spec, we should perform preprocessing here.
     // See: http://dev.w3.org/csswg/css-syntax/#input-preprocessing
     //
     // However, we can skip this step since:
     // * We're using HTML spaces (which accept \r and \f as a valid white space)
     // * Do not count white spaces
     // * consumeEscape replaces NULLs for replacement characters
 
+    if (string.isEmpty())
+        return;
+
     MediaQueryInputStream input(string);
     MediaQueryTokenizer tokenizer(input);
     while (true) {
         MediaQueryToken token = tokenizer.nextToken();
         outTokens.append(token);
         if (token.type() == EOFToken)
             return;
     }
 }
 
@@ skipping 269 matching lines @@
     if (firstChar == '-') {
         if (isNameStart(m_input.peek(1)))
             return true;
         return nextTwoCharsAreValidEscape(1);
     }
 
     return false;
 }
 
 } // namespace WebCore