[date] Add ICU backend for timezone info behind a flag

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/base/timezone-cache.h"
@@ skipping 21 matching lines @@
   // Conservative upper bound on time that can be stored in JSDate
   // before UTC conversion.
   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();
-  }
+  DateCache();
 
   virtual ~DateCache() {
     delete tz_cache_;
     tz_cache_ = NULL;
   }
 
 
   // Clears cached timezone information and increments the cache stamp.
   void ResetDateCache();
 
@@ skipping 230 matching lines @@
   const char* tz_name_;
   const char* dst_tz_name_;
 
   base::TimezoneCache* tz_cache_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif