[foozzie] Make mock for random more expressive

Bug: chromium:1044942
Change-Id: If7caf955f5aab954a57c46aab7830830b1a64d04
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2162872Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67374}

test/mjsunit/tools/foozzie.js

@@ -8,9 +8,9 @@
 // Test foozzie mocks for differential fuzzing.
 
 // Deterministic Math.random.
-assertEquals(0.1, Math.random());
-assertEquals(0.2, Math.random());
-assertEquals(0.3, Math.random());
+assertEquals(0.7098480789645691, Math.random());
+assertEquals(0.9742682568175951, Math.random());
+assertEquals(0.20008059867222983, Math.random());
 
 // Deterministic date.
 assertEquals(1477662728698, Date.now());

tools/clusterfuzz/v8_mock.js

@@ -14,10 +14,10 @@ var prettyPrinted = function prettyPrinted(msg) { return msg; };
 
 // Mock Math.random.
 (function() {
-  let index = 0
+  let index = 1;
   Math.random = function() {
-    index = (index + 1) % 10;
-    return index / 10.0;
+      const x = Math.sin(index++) * 10000;
+      return x - Math.floor(x);
   }
 })();