Default to UTC in the legacy date parser.

src/dateparser-inl.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 160 matching lines @@
         tz.SetAbsoluteMinute(n % 100);
       }
     } else if ((token.IsAsciiSign() || token.IsSymbol(')')) &&
                has_read_number) {
       // Extra sign or ')' is illegal if a number has been read.
       return false;
     } else {
       // Ignore other characters and whitespace.
     }
   }
-
+  // Successfully parsed ES5 Date Time String. Default to UTC if no TZ given.
+  if (tz.IsEmpty()) tz.Set(0);
   return day.Write(out) && time.Write(out) && tz.Write(out);
 }
 
 
 template<typename CharType>
 DateParser::DateToken DateParser::DateStringTokenizer<CharType>::Scan() {
   int pre_pos = in_->position();
   if (in_->IsEnd()) return DateToken::EndOfInput();
   if (in_->IsAsciiDigit()) {
     int n = in_->ReadUnsignedNumeral();
@@ skipping 133 matching lines @@
   // Successfully parsed ES5 Date Time String. Default to UTC if no TZ given.
   if (tz->IsEmpty()) tz->Set(0);
   day->set_iso_date();
   return DateToken::EndOfInput();
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_DATEPARSER_INL_H_