MiniJsParser: fix a regression + support computed props + add tests

test/js/builder_test.dart

+import 'package:dev_compiler/src/js/js_ast.dart';
+import 'package:test/test.dart';
+
+final _prenumberedPlaceholders = new RegExp(r'#\d+');
+
+_parser(String src) =>
+    new MiniJsParser(src.replaceAll(_prenumberedPlaceholders, '#'));
+
+_check(Node node, String expected) =>
+    expect(node.toString(), 'js_ast `$expected`');
+
+_checkStatement(String src) =>
+    _check(_parser(src).parseStatement(), src);
+
+_checkExpression(String src) =>
+    _check(_parser(src).parseExpression(), src);
+
+main() {
+  group('MiniJsParser', () {
+    // TODO(ochafik): Add more coverage.
+    test('parses classes with complex members', () {
+      _checkExpression(
+          'class Foo {\n'
+          '  [foo](...args) {}\n'
+          '  [#0](x) {}\n'
+          '  static [foo](...args) {}\n'
+          '  static [#1](x) {}\n'
+          '  get [foo]() {}\n'
+          '  get [#2]() {}\n'
+          '  static get [foo]() {}\n'
+          '  static get [#3]() {}\n'
+          '  set [foo](v) {}\n'
+          '  set [#4](v) {}\n'
+          '  static set [foo](v) {}\n'
+          '  static set [#5](v) {}\n'
+          '}');
+    });
+    test('parses statements', () {
+      _checkStatement('for (let i = 0; i < 10; i++) {\n}\n');
+      _checkStatement('for (let i = 0, j = 1; i < 10; i++) {\n}\n');
+      _checkStatement('var [x, y = []] = list;\n');
+      _checkStatement('var {x, y = {x: y}} = obj;\n');
+    });
+  });
+}