[Math] implement Math.random as TFJ builtin.

src/factory.cc

Index: src/factory.cc
diff --git a/src/factory.cc b/src/factory.cc
index 1f2c868faa90d08badf33920297686493e14a1e0..877818a29b7bd4884b5933dab196c194caaf4922 100644
--- a/src/factory.cc
+++ b/src/factory.cc
@@ -780,6 +780,7 @@ Handle<Context> Factory::NewNativeContext() {
   Handle<Context> context = Handle<Context>::cast(array);
   context->set_native_context(*context);
   context->set_errors_thrown(Smi::kZero);
+  context->set_math_random_index(Smi::kZero);
   Handle<WeakCell> weak_cell = NewWeakCell(context);
   context->set_self_weak_cell(*weak_cell);
   DCHECK(context->IsNativeContext());