[es6] disable optimization in lazily parsed arrows with rest params

src/parser.cc

Index: src/parser.cc
diff --git a/src/parser.cc b/src/parser.cc
index 55b4122d71f8cbcccc2d04e8c5d494ef01e508a1..26c187292011337bb265bfa51476aee319b32c4e 100644
--- a/src/parser.cc
+++ b/src/parser.cc
@@ -1216,6 +1216,10 @@ FunctionLiteral* Parser::ParseLazy(Isolate* isolate, ParseInfo* info,
             // must produce a FunctionLiteral.
             DCHECK(expression->IsFunctionLiteral());
             result = expression->AsFunctionLiteral();
+            if (scope->has_rest_parameter()) {
+              // TODO(caitp): enable optimization of functions with rest params
+              result->set_dont_optimize_reason(kRestParameter);
+            }
           } else {
             ok = false;
           }