restore arrow function bind this workaround

lib/src/js/precedence.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library precedence;
 
 const EXPRESSION = 0;
 const SPREAD = EXPRESSION + 1;
 const YIELD = SPREAD + 1;
+
+// Note that some primary expressions (in the parser) must be emitted with lower
+// precedence, because it's not normally legal for them to be followed by
+// other postfix expressions, like ACCESS and CALL. For example:
+// `function foo(){}` needs parens to call or access properties or
+// compare with equality. Same thing with `class Foo {}` and `(x) => x`.
+// However, prefix unary expressions will work in these cases. Unfortunately our
+// current precedence tracking doesn't capture this distinction.
+const PRIMARY_LOW_PRECEDENCE = ASSIGNMENT;
+
 const ASSIGNMENT = YIELD + 1;
 const LOGICAL_OR = ASSIGNMENT + 1;
 const LOGICAL_AND = LOGICAL_OR + 1;
 const BIT_OR = LOGICAL_AND + 1;
 const BIT_XOR = BIT_OR + 1;
 const BIT_AND = BIT_XOR + 1;
 const EQUALITY = BIT_AND + 1;
 const RELATIONAL = EQUALITY + 1;
 const SHIFT = RELATIONAL + 1;
 const ADDITIVE = SHIFT + 1;
 const MULTIPLICATIVE = ADDITIVE + 1;
 const UNARY = MULTIPLICATIVE + 1;
 const LEFT_HAND_SIDE = UNARY + 1;
 const CALL = LEFT_HAND_SIDE;
 // We always emit `new` with parenthesis, so it uses ACCESS as its precedence.
 const ACCESS = CALL + 1;
 const PRIMARY = ACCESS + 1;