Update dart2js parser to disallow repeated comparisons and prefix +.

sdk/lib/_internal/compiler/implementation/warnings.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.
 
 part of dart2js;
 
 const DONT_KNOW_HOW_TO_FIX = "";
 
 /**
  * The messages in this file should meet the following guide lines:
@@ skipping 797 matching lines @@
 
 main() => foo(1);
 """]);
 
   static const MessageKind CONST_WITHOUT_INITIALIZER = const MessageKind(
       "Error: A constant variable must be initialized.",
       howToFix: "Try adding an initializer or "
                 "removing the 'const' modifier.",
       examples: const ["""
 void main() {
-  const c; // This constant variable must be initialized. 
+  const c; // This constant variable must be initialized.
 }"""]);
 
   static const MessageKind MEMBER_USES_CLASS_NAME = const MessageKind(
       "Error: Member variable can't have the same name as the class it is "
       "declared in.",
       howToFix: "Try renaming the variable.",
       examples: const ["""
 class A { var A; }
 main() {
   var a = new A();
@@ skipping 79 matching lines @@
       'Error: Library not found "#{resolvedUri}".');
 
   static const MessageKind UNSUPPORTED_EQ_EQ_EQ = const MessageKind(
       'Error: "===" is not an operator. '
       'Did you mean "#{lhs} == #{rhs}" or "identical(#{lhs}, #{rhs})"?');
 
   static const MessageKind UNSUPPORTED_BANG_EQ_EQ = const MessageKind(
       'Error: "!==" is not an operator. '
       'Did you mean "#{lhs} != #{rhs}" or "!identical(#{lhs}, #{rhs})"?');
 
+  static const MessageKind UNSUPPORTED_PREFIX_PLUS = const MessageKind(
+      "Error: '+' is not a prefix operator. ",
+      howToFix: "Try removing '+'.",
+      examples: const [ "+2  // No longer a valid way to write '2'" ]);
+
   static const MessageKind UNSUPPORTED_THROW_WITHOUT_EXP = const MessageKind(
       'Error: No expression after "throw". '
       'Did you mean "rethrow"?');
 
   static const MessageKind MIRRORS_EXPECTED_STRING = const MessageKind(
       "Hint: Can't use '#{name}' here because it's an instance of '#{type}' "
       "and a 'String' value is expected.",
       howToFix: "Did you forget to add quotes?",
       examples: const [
           """
@@ skipping 364 matching lines @@
 
 class CompileTimeConstantError extends Diagnostic {
   CompileTimeConstantError(MessageKind kind, Map arguments, bool terse)
     : super(kind, arguments, terse);
 }
 
 class CompilationError extends Diagnostic {
   CompilationError(MessageKind kind, Map arguments, bool terse)
     : super(kind, arguments, terse);
 }