Use ExpressionClassifier to identify valid arrow function formals

src/parser.h

Index: src/parser.h
diff --git a/src/parser.h b/src/parser.h
index 2b0a4d92211a4e119f15e36164ad1aaf3cdd7432..26fbed6a216f807fa48ded6fbe556361fa593e22 100644
--- a/src/parser.h
+++ b/src/parser.h
@@ -760,11 +760,13 @@ class ParserTraits {
 
   void DeclareArrowFunctionParameters(Scope* scope, Expression* expr,
                                       const Scanner::Location& params_loc,
-                                      FormalParameterErrorLocations* error_locs,
+                                      Scanner::Location* duplicate_loc,
                                       bool* ok);
-  void ParseArrowFunctionFormalParameters(
-      Scope* scope, Expression* params, const Scanner::Location& params_loc,
-      FormalParameterErrorLocations* error_locs, bool* is_rest, bool* ok);
+  void ParseArrowFunctionFormalParameters(Scope* scope, Expression* params,
+                                          const Scanner::Location& params_loc,
+                                          bool* is_rest,
+                                          Scanner::Location* duplicate_loc,
+                                          bool* ok);
 
   // Temporary glue; these functions will move to ParserBase.
   Expression* ParseV8Intrinsic(bool* ok);