Make built-ins strict mode conforming, and support a --use-strict flag.

src/date.js

 // Copyright 2006-2008 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 10 matching lines @@
 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 
 // This file relies on the fact that the following declarations have been made
 // in v8natives.js:
-// const $isFinite = GlobalIsFinite;
+// var $isFinite = GlobalIsFinite;
 
 // -------------------------------------------------------------------
 
 // This file contains date support implemented in JavaScript.
 
-
 // Keep reference to original values of some global properties.  This
 // has the added benefit that the code in this file is isolated from
 // changes to these properties.
-const $Date = global.Date;
+var $Date = global.Date;
 
 // Helper function to throw error.
 function ThrowDateTypeError() {
   throw new $TypeError('this is not a Date object.');
 }
 
 // ECMA 262 - 5.2
 function Modulo(value, remainder) {
   var mod = value % remainder;
   // Guard against returning -0.
@@ skipping 1065 matching lines @@
     "toGMTString", DateToGMTString,
     "toUTCString", DateToUTCString,
     "getYear", DateGetYear,
     "setYear", DateSetYear,
     "toISOString", DateToISOString,
     "toJSON", DateToJSON
   ));
 }
 
 SetUpDate();