[Math] implement Math.random as TFJ builtin.

src/snapshot/partial-serializer.cc

Index: src/snapshot/partial-serializer.cc
diff --git a/src/snapshot/partial-serializer.cc b/src/snapshot/partial-serializer.cc
index b46f6755f0badab8e01e85b8b2eba317aeec724e..d192f51d6f676eda03b748055019ec2bd51a4b80 100644
--- a/src/snapshot/partial-serializer.cc
+++ b/src/snapshot/partial-serializer.cc
@@ -33,6 +33,9 @@ void PartialSerializer::Serialize(Object** o) {
       context->set(Context::NEXT_CONTEXT_LINK,
                    isolate_->heap()->undefined_value());
       DCHECK(!context->global_object()->IsUndefined(context->GetIsolate()));
+      // Reset math random cache to get fresh random numbers.
+      context->set_math_random_index(Smi::kZero);
+      context->set_math_random_cache(isolate_->heap()->undefined_value());
     }
   }
   VisitPointer(o);