Statically check for assignments to const in harmony mode.

src/parser.h

Index: src/parser.h
diff --git a/src/parser.h b/src/parser.h
index e13b120fa69baea2f9fbc5b663268b9ea0d74b07..023dc584428fd77c5519ca5d4838a7973214b34a 100644
--- a/src/parser.h
+++ b/src/parser.h
@@ -651,6 +651,10 @@ class Parser {
                                                bool* is_set,
                                                bool* ok);
 
+  // Determine if the expression is a variable proxy and mark it as being used
+  // in an assignment or with a increment/decrement operator.
+  void MarkAsUsedAsLValue(Expression* expression);
+
   // Strict mode validation of LValue expressions
   void CheckStrictModeLValue(Expression* expression,
                              const char* error,