[fix][babel-plugin-transform-es2015-parameters] arguments.length optimization bugfix

packages/babel-plugin-transform-es2015-parameters/test/fixtures/parameters/rest-member-expression-deoptimisation/actual.js

@@ -32,3 +32,11 @@ var b = function (foo, ...bar) {
 var b = function (...bar) {
   return bar.len;
 };
+
+var b = function (foo, ...bar) {
+  return bar.length * 2;
+};
+
+var b = function (foo, baz, ...bar) {
+  return bar.length;
+};

packages/babel-plugin-transform-es2015-parameters/test/fixtures/parameters/rest-member-expression-deoptimisation/expected.js

@@ -61,3 +61,11 @@ var b = function () {
 
   return bar.len;
 };
+
+var b = function (foo) {
+  return (arguments.length - 1) * 2;
+};
+
+var b = function (foo, baz) {
+  return arguments.length - 2;
+};