[es6] support AssignmentPattern as LHS in for-in/of loops

src/parsing/preparser.cc

Index: src/parsing/preparser.cc
diff --git a/src/parsing/preparser.cc b/src/parsing/preparser.cc
index acb6b33750d4597de19b65bd0a39d7f7ddde7348..a9af4a955884511de1fc0e3eabc3953c0baa0073 100644
--- a/src/parsing/preparser.cc
+++ b/src/parsing/preparser.cc
@@ -956,15 +956,29 @@ PreParser::Statement PreParser::ParseForStatement(bool* ok) {
       }
     } else {
       int lhs_beg_pos = peek_position();
-      Expression lhs = ParseExpression(false, CHECK_OK);
+      ExpressionClassifier classifier;
+      Expression lhs = ParseExpression(false, &classifier, CHECK_OK);
       int lhs_end_pos = scanner()->location().end_pos;
       is_let_identifier_expression =
           lhs.IsIdentifier() && lhs.AsIdentifier().IsLet();
-      if (CheckInOrOf(&mode, ok)) {
-        if (!*ok) return Statement::Default();
-        lhs = CheckAndRewriteReferenceExpression(
-            lhs, lhs_beg_pos, lhs_end_pos, MessageTemplate::kInvalidLhsInFor,
-            kSyntaxError, CHECK_OK);
+      bool is_for_each = CheckInOrOf(&mode, ok);
+      if (!*ok) return Statement::Default();
+      bool is_destructuring = is_for_each &&
+                              allow_harmony_destructuring_assignment() &&
+                              (lhs->IsArrayLiteral() || lhs->IsObjectLiteral());
+
+      if (is_destructuring) {
+        ValidateAssignmentPattern(&classifier, CHECK_OK);
+      } else {
+        ValidateExpression(&classifier, CHECK_OK);
+      }
+
+      if (is_for_each) {
+        if (!is_destructuring) {
+          lhs = CheckAndRewriteReferenceExpression(
+              lhs, lhs_beg_pos, lhs_end_pos, MessageTemplate::kInvalidLhsInFor,
+              kSyntaxError, CHECK_OK);
+        }
         ParseExpression(true, CHECK_OK);
         Expect(Token::RPAREN, CHECK_OK);
         ParseSubStatement(CHECK_OK);