[foozzie] More robust Date mock

Later manipulation of Array.prototype.concat could lead to calling the Date constructor with empty arguments list. This let a non-mocked date slip in.

BUG=chromium:698097
NOTRY=true
TBR=yangguo@chromium.org,mstarzinger@chromium.org

Change-Id: Ib4bd97e06ea7be8c32d0057d42943f9f82ea6b5f
Reviewed-on: https://chromium-review.googlesource.com/449732Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43570}

tools/foozzie/v8_mock.js

@@ -31,11 +31,13 @@ var __PrettyPrint = function __PrettyPrint(msg) { print(msg); };
     return mockDate
   }
 
+  var origConcat = Array.prototype.concat
   var origDate = Date;
   var constructDate = function(args) {
     if (args.length > 0) {
       var result = new (
-          Function.prototype.bind.apply(origDate, [null].concat(args)));
+          Function.prototype.bind.apply(
+              origDate, origConcat.apply([null], args)));
     } else {
       var result = new origDate(mockDateNow());
     }