Avoid temporary Vectors for arrow function parameter lists

src/parser.h

Index: src/parser.h
diff --git a/src/parser.h b/src/parser.h
index 3b3450c2398d1bbbf89a92cd746e9f1dd12f2010..30527b0406b0cf6ca9345f3edd4d9d16654579ab 100644
--- a/src/parser.h
+++ b/src/parser.h
@@ -550,8 +550,10 @@ class ParserTraits {
   V8_INLINE Scope* NewScope(Scope* parent_scope, ScopeType scope_type);
 
   // Utility functions
-  Vector<VariableProxy*> ParameterListFromExpression(Expression* expression,
-                                                     bool* ok);
+  unsigned DeclareArrowParametersFromExpression(Expression* expression,
+                                                Scope* scope,
+                                                Scanner::Location* dupe_loc,
+                                                bool* ok);
   V8_INLINE AstValueFactory* ast_value_factory();
 
   // Temporary glue; these functions will move to ParserBase.