Use identical in token operators.

pkg/front_end/lib/src/fasta/scanner/token.dart

 // Copyright (c) 2011, 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 fasta.scanner.token;
 
 import 'dart:collection' show
     HashSet;
 
 import 'dart:convert' show
@@ skipping 332 matching lines @@
       : super.internal();
 }
 
 bool isUserDefinableOperator(String value) {
   return isBinaryOperator(value) ||
       isMinusOperator(value) ||
       isTernaryOperator(value) ||
       isUnaryOperator(value);
 }
 
-bool isUnaryOperator(String value) => value == '~';
+bool isUnaryOperator(String value) => identical(value, "~");
 
 bool isBinaryOperator(String value) {
-  return value == '==' ||
-      value == '[]' ||
-      value == '*' ||
-      value == '/' ||
-      value == '%' ||
-      value == '~/' ||
-      value == '+' ||
-      value == '<<' ||
-      value == '>>' ||
-      value == '>=' ||
-      value == '>' ||
-      value == '<=' ||
-      value == '<' ||
-      value == '&' ||
-      value == '^' ||
-      value == '|';
+  return identical(value, "==") ||
+      identical(value, "[]") ||
+      identical(value, "*") ||
+      identical(value, "/") ||
+      identical(value, "%") ||
+      identical(value, "~/") ||
+      identical(value, "+") ||
+      identical(value, "<<") ||
+      identical(value, ">>") ||
+      identical(value, ">=") ||
+      identical(value, ">") ||
+      identical(value, "<=") ||
+      identical(value, "<") ||
+      identical(value, "&") ||
+      identical(value, "^") ||
+      identical(value, "|");
 }
 
-bool isTernaryOperator(String value) => value == '[]=';
+bool isTernaryOperator(String value) => identical(value, "[]=");
 
-bool isMinusOperator(String value) => value == '-';
+bool isMinusOperator(String value) => identical(value, "-");