Enable zero length source size in sizes attribute

Source/core/css/parser/SizesAttributeParserTest.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/SizesAttributeParser.h"
 
 #include "core/css/MediaValuesCached.h"
 
 #include <gtest/gtest.h>
@@ skipping 12 matching lines @@
     // Otherwise, the output string is identical to the first string.
     TestCase testCases[] = {
         {"screen", 500},
         {"(min-width:500px)", 500},
         {"(min-width:500px) 200px", 200},
         {"(min-width:500px) 50vw", 250},
         {"(min-width:500px) 200px, 400px", 200},
         {"400px, (min-width:500px) 200px", 400},
         {"(min-width:5000px) 200px, 400px", 400},
         {"(blalbadfsdf) 200px, 400px", 400},
-        {"0", 500},
-        {"-0", 500},
+        {"0", 0},
+        {"-0", 0},
         {"1", 500},
         {"300px, 400px", 300},
         {"(min-width:5000px) 200px, (min-width:500px) 400px", 400},
         {"", 500},
         {"  ", 500},
         {" /**/ ", 500},
         {" /**/ 300px", 300},
         {"300px /**/ ", 300},
         {" /**/ (min-width:500px) /**/ 300px", 300},
         {"-100px, 200px", 200},
@@ skipping 28 matching lines @@
     data.strictMode = true;
     RefPtr<MediaValues> mediaValues = MediaValuesCached::create(data);
 
     for (unsigned i = 0; testCases[i].input; ++i) {
         int effectiveSize = SizesAttributeParser::findEffectiveSize(testCases[i].input, mediaValues);
         ASSERT_EQ(testCases[i].output, effectiveSize);
     }
 }
 
 } // namespace