[foozzie] Mock out measureMemory for correctness fuzzing

No-Try: true
Bug: chromium:1023247
Change-Id: I23abb26425d7adcd69d07af906738a69bac8688d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1906380
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64871}

tools/clusterfuzz/v8_mock.js

@@ -78,9 +78,10 @@ var prettyPrinted = function prettyPrinted(msg) { return msg; };
   Date = new Proxy(Date, handler);
 })();
 
-// Mock performace.now().
+// Mock performace methods.
 (function () {
   performance.now = function () { return 1.2; }
+  performance.measureMemory = function () { return []; }
 })();
 
 // Mock stack traces.