Fix 'illegal access' in Date constructor edge case

src/date.h

 // Copyright 2012 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.
 
 #ifndef V8_DATE_H_
 #define V8_DATE_H_
 
 #include "src/allocation.h"
 #include "src/base/platform/platform.h"
 #include "src/globals.h"
 
 
 namespace v8 {
 namespace internal {
 
 class DateCache {
  public:
   static const int kMsPerMin = 60 * 1000;
   static const int kSecPerDay = 24 * 60 * 60;
   static const int64_t kMsPerDay = kSecPerDay * 1000;
+  static const int64_t kMsPerMonth = kMsPerDay * 30;
 
   // The largest time that can be passed to OS date-time library functions.
   static const int kMaxEpochTimeInSec = kMaxInt;
   static const int64_t kMaxEpochTimeInMs =
       static_cast<int64_t>(kMaxInt) * 1000;
 
   // The largest time that can be stored in JSDate.
   static const int64_t kMaxTimeInMs =
       static_cast<int64_t>(864000000) * 10000000;
 
   // Conservative upper bound on time that can be stored in JSDate
   // before UTC conversion.
-  static const int64_t kMaxTimeBeforeUTCInMs =
-      kMaxTimeInMs + 10 * kMsPerDay;
+  static const int64_t kMaxTimeBeforeUTCInMs = kMaxTimeInMs + kMsPerMonth;
 
   // Sentinel that denotes an invalid local offset.
   static const int kInvalidLocalOffsetInMs = kMaxInt;
   // Sentinel that denotes an invalid cache stamp.
   // It is an invariant of DateCache that cache stamp is non-negative.
   static const int kInvalidStamp = -1;
 
   DateCache() : stamp_(0), tz_cache_(base::OS::CreateTimezoneCache()) {
     ResetDateCache();
   }
@@ skipping 228 matching lines @@
   int ymd_month_;
   int ymd_day_;
 
   base::TimezoneCache* tz_cache_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif