Update dart2js parser to disallow repeated comparisons and prefix +.

sdk/lib/_internal/compiler/implementation/warnings.dart

Index: sdk/lib/_internal/compiler/implementation/warnings.dart
diff --git a/sdk/lib/_internal/compiler/implementation/warnings.dart b/sdk/lib/_internal/compiler/implementation/warnings.dart
index bd06786f895183766f130b48cb048047c567f3ec..54cbe3170396ad7e79c245ba4bd45f975fe862a4 100644
--- a/sdk/lib/_internal/compiler/implementation/warnings.dart
+++ b/sdk/lib/_internal/compiler/implementation/warnings.dart
@@ -815,7 +815,7 @@ main() => foo(1);
                 "removing the 'const' modifier.",
       examples: const ["""
 void main() {
-  const c; // This constant variable must be initialized. 
+  const c; // This constant variable must be initialized.
 }"""]);
 
 
@@ -901,6 +901,9 @@ Error: "#{value}" is not a valid Symbol name because is not:
       '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.');

[ahe, 2013/09/20 08:17:17]

Could you add an example and "howToFix"?

[Lasse Reichstein Nielsen, 2013/09/20 08:26:15]

What would a fix be?
For "+2" it would just be removing the "+". Any other case of using + as a
prefix is some kind of error that is hard to predict.

[ahe, 2013/09/20 08:33:42]

I think something like:

"Try removing '+'."

[ahe, 2013/09/20 08:33:42]

Another thing, please use double quotes for the complete message and single
quotes for substrings. The logic is that Google ignores single quotes in
searches.

+
   static const MessageKind UNSUPPORTED_THROW_WITHOUT_EXP = const MessageKind(
       'Error: No expression after "throw". '
       'Did you mean "rethrow"?');