[date] Date parser says true even for wrong dates, check twice.

R=yangguo@chromium.org
BUG=chromium:575082
LOG=n

Review URL: https://codereview.chromium.org/1566973002

Cr-Commit-Position: refs/heads/master@{#33149}

src/builtins.cc

@@ -2096,7 +2096,9 @@ double ParseDateTimeString(Handle<String> str) {
                                tmp->get(5)->Number(), tmp->get(6)->Number());
   double date = MakeDate(day, time);
   if (tmp->get(7)->IsNull()) {
+    if (!std::isnan(date)) {
       date = isolate->date_cache()->ToUTC(static_cast<int64_t>(date));
+    }
   } else {
     date -= tmp->get(7)->Number() * 1000.0;
   }

src/date.cc

@@ -71,7 +71,7 @@ void DateCache::YearMonthDayFromDays(
   *year = 400 * (days / kDaysIn400Years) - kYearsOffset;
   days %= kDaysIn400Years;
 
-  DCHECK(DaysFromYearMonth(*year, 0) + days == save_days);
+  DCHECK_EQ(save_days, DaysFromYearMonth(*year, 0) + days);
 
   days--;
   int yd1 = days / kDaysIn100Years;

test/mjsunit/regress/regress-crbug-575082.js

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+var y = new Date("-1073741824");