Use SizesAttributeParser to get the right srcset resource

Source/core/css/parser/SizesAttributeParser.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 "SizesAttributeParser.h"
 
 #include "MediaTypeNames.h"
 #include "core/css/MediaQueryEvaluator.h"
 #include "core/css/parser/MediaQueryTokenizer.h"
@@ skipping 11 matching lines @@
     return parser.effectiveSize();
 }
 
 bool SizesAttributeParser::calculateLengthInPixels(TokenIterator startToken, TokenIterator endToken, unsigned& result)
 {
     MediaQueryTokenType type = startToken->type();
     if (type == DimensionToken) {
         int length;
         if (!CSSPrimitiveValue::isLength(startToken->unitType()))
             return false;
-        if (m_mediaValues->computeLength(startToken->numericValue(), startToken->unitType(), length)) {
-            if (length > 0) {
-                result = (unsigned)length;
-                return true;
-            }
+        if ((m_mediaValues->computeLength(startToken->numericValue(), startToken->unitType(), length)) && (length > 0)) {
+            result = (unsigned)length;
+            return true;
         }
     }
-    if (type == FunctionToken) {
-        // FIXME - Handle calc() functions here!
-    }
+    // FIXME - Handle calc() FunctionToken here!
     return false;
 }
 
 static void reverseSkipIrrelevantTokens(TokenIterator& token, TokenIterator startToken)
 {
     TokenIterator endToken = token;
     while (token != startToken && (token->type() == WhitespaceToken || token->type() == CommentToken || token->type() == EOFToken))
         --token;
     if (token != endToken)
         ++token;
@@ skipping 42 matching lines @@
     RefPtrWillBeRawPtr<MediaQuerySet> mediaCondition = MediaQueryParser::parseMediaCondition(startToken, endToken);
     if (mediaCondition && mediaConditionMatches(mediaCondition)) {
         m_length = length;
         return true;
     }
     return false;
 }
 
 bool SizesAttributeParser::parse(Vector<MediaQueryToken>& tokens)
 {
+    if (tokens.isEmpty())
+        return false;
     TokenIterator startToken = tokens.begin();
     TokenIterator endToken;
     // Split on a comma token, and send the result tokens to be parsed as (media-condition, length) pairs
     for (TokenIterator token = tokens.begin(); token != tokens.end(); ++token) {
         if (token->type() == CommaToken) {
             endToken = token;
             if (parseMediaConditionAndLength(startToken, endToken))
                 return true;
             startToken = token;
             ++startToken;
@@ skipping 11 matching lines @@
 }
 
 unsigned SizesAttributeParser::effectiveSizeDefaultValue()
 {
     // Returning the equivalent of "100%"
     return m_mediaValues->viewportWidth();
 }
 
 } // namespace