Enable zero length source size in sizes attribute

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"
 #include "core/css/parser/SizesCalcParser.h"
 
 namespace WebCore {
 
 unsigned SizesAttributeParser::findEffectiveSize(const String& attribute, PassRefPtr<MediaValues> mediaValues)
 {
     Vector<MediaQueryToken> tokens;
     SizesAttributeParser parser(mediaValues);
 
     MediaQueryTokenizer::tokenize(attribute, tokens);
     if (!parser.parse(tokens))
         return parser.effectiveSizeDefaultValue();
     return parser.effectiveSize();
 }
 
 bool SizesAttributeParser::calculateLengthInPixels(MediaQueryTokenIterator startToken, MediaQueryTokenIterator endToken, unsigned& result)
 {
+    if (startToken == endToken)
+        return false;
     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)) && (length > 0)) {
             result = (unsigned)length;
             return true;
         }
     } else if (type == FunctionToken) {
         return SizesCalcParser::parse(startToken, endToken, m_mediaValues, result);
+    } else if (type == NumberToken && !startToken->numericValue()) {
+        result = 0;
+        return true;
     }
 
     return false;
 }
 
 static void reverseSkipIrrelevantTokens(MediaQueryTokenIterator& token, MediaQueryTokenIterator startToken)
 {
     MediaQueryTokenIterator endToken = token;
     while (token != startToken && (token->type() == WhitespaceToken || token->type() == CommentToken || token->type() == EOFToken))
         --token;
@@ skipping 37 matching lines @@
     reverseSkipIrrelevantTokens(endToken, startToken);
     lengthTokenEnd = endToken;
     reverseSkipUntilComponentStart(endToken, startToken);
     lengthTokenStart = endToken;
     unsigned length;
     if (!calculateLengthInPixels(lengthTokenStart, lengthTokenEnd, length))
         return false;
     RefPtrWillBeRawPtr<MediaQuerySet> mediaCondition = MediaQueryParser::parseMediaCondition(startToken, endToken);
     if (mediaCondition && mediaConditionMatches(mediaCondition)) {
         m_length = length;
+        m_lengthWasSet = true;
         return true;
     }
     return false;
 }
 
 bool SizesAttributeParser::parse(Vector<MediaQueryToken>& tokens)
 {
     if (tokens.isEmpty())
         return false;
     MediaQueryTokenIterator startToken = tokens.begin();
     MediaQueryTokenIterator endToken;
     // Split on a comma token, and send the result tokens to be parsed as (media-condition, length) pairs
     for (MediaQueryTokenIterator token = tokens.begin(); token != tokens.end(); ++token) {
         if (token->type() == CommaToken) {
             endToken = token;
             if (parseMediaConditionAndLength(startToken, endToken))
                 return true;
             startToken = token;
             ++startToken;
         }
     }
     endToken = tokens.end();
     return parseMediaConditionAndLength(startToken, --endToken);
 }
 
 unsigned SizesAttributeParser::effectiveSize()
 {
-    if (m_length)
+    if (m_lengthWasSet)
         return m_length;
     return effectiveSizeDefaultValue();
 }
 
 unsigned SizesAttributeParser::effectiveSizeDefaultValue()
 {
     // Returning the equivalent of "100%"
     return m_mediaValues->viewportWidth();
 }
 
 } // namespace