[foozzie] Make date mock more reliable.

TBR=mathias@chromium.org

Bug: chromium:1054390
Change-Id: I9533a0ca0faa0afa7032aa7dde144df48408c9d5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2066958Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66377}

tools/clusterfuzz/v8_mock.js

@@ -32,10 +32,11 @@ var prettyPrinted = function prettyPrinted(msg) { return msg; };
   }
 
   const origDate = Date;
+  const construct = Reflect.construct;
   const constructDate = function(args) {
     let result;
     if (args.length) {
-      result = new origDate(...args);
+      result = construct(origDate, args);
     } else {
       result = new origDate(mockDateNow());
     }