For-of statements do not permit initializers.

src/preparser.cc

Index: src/preparser.cc
diff --git a/src/preparser.cc b/src/preparser.cc
index 828177aee0a696ddf51c75b2ca7867aacc163522..3268e3c508bc2fb6887564b5d03e5675c2f46d2a 100644
--- a/src/preparser.cc
+++ b/src/preparser.cc
@@ -659,10 +659,9 @@ PreParser::Statement PreParser::ParseWhileStatement(bool* ok) {
 }
 
 
-bool PreParser::CheckInOrOf() {
+bool PreParser::CheckInOrOf(bool accept_OF) {
   if (peek() == i::Token::IN ||
-      (allow_for_of() &&
-       peek() == i::Token::IDENTIFIER &&
+      (allow_for_of() && accept_OF && peek() == i::Token::IDENTIFIER &&
        scanner_->is_next_contextual_keyword(v8::internal::CStrVector("of")))) {
     Next();
     return true;
@@ -685,9 +684,10 @@ PreParser::Statement PreParser::ParseForStatement(bool* ok) {
       VariableDeclarationProperties decl_props = kHasNoInitializers;
       ParseVariableDeclarations(
           kForStatement, &decl_props, &decl_count, CHECK_OK);
-      bool accept_IN = decl_count == 1 &&
-          !(is_let && decl_props == kHasInitializers);
-      if (accept_IN && CheckInOrOf()) {
+      bool has_initializers = decl_props == kHasInitializers;
+      bool accept_IN = decl_count == 1 && !(is_let && has_initializers);
+      bool accept_OF = !has_initializers;
+      if (accept_IN && CheckInOrOf(accept_OF)) {
         ParseExpression(true, CHECK_OK);
         Expect(i::Token::RPAREN, CHECK_OK);
 
@@ -695,8 +695,8 @@ PreParser::Statement PreParser::ParseForStatement(bool* ok) {
         return Statement::Default();
       }
     } else {
-      ParseExpression(false, CHECK_OK);
-      if (CheckInOrOf()) {
+      Expression lhs = ParseExpression(false, CHECK_OK);
+      if (CheckInOrOf(lhs.IsIdentifier())) {
         ParseExpression(true, CHECK_OK);
         Expect(i::Token::RPAREN, CHECK_OK);