Fix bug in parser that allows "(foo):42" as a labeled statement.

src/parser.cc

Index: src/parser.cc
diff --git a/src/parser.cc b/src/parser.cc
index a0f3b7147f20eda1457d4f41276c550d70b2b612..515eff3fb5428ff53ab0012fa51e38f379b4c109 100644
--- a/src/parser.cc
+++ b/src/parser.cc
@@ -1692,11 +1692,13 @@ Statement* Parser::ParseExpressionOrLabelledStatement(ZoneStringList* labels,
   // ExpressionStatement | LabelledStatement ::
   //   Expression ';'
   //   Identifier ':' Statement
-
+  bool starts_with_idenfifier = (peek() == Token::IDENTIFIER);
   Expression* expr = ParseExpression(true, CHECK_OK);
-  if (peek() == Token::COLON && expr &&
+  if (peek() == Token::COLON && starts_with_idenfifier && expr &&
       expr->AsVariableProxy() != NULL &&
       !expr->AsVariableProxy()->is_this()) {
+    // Expression is a single identifier, and not, e.g., a parenthesized
+    // identifier.
     VariableProxy* var = expr->AsVariableProxy();
     Handle<String> label = var->name();
     // TODO(1240780): We don't check for redeclaration of labels