Changes dart2js to warn at reified usage of method type variables.

pkg/compiler/lib/src/diagnostics/messages.dart

Index: pkg/compiler/lib/src/diagnostics/messages.dart
diff --git a/pkg/compiler/lib/src/diagnostics/messages.dart b/pkg/compiler/lib/src/diagnostics/messages.dart
index 830a010ad396a68d44db01c3a90f7fa02f092978..ba2ca1f04316a3caf82cce1314291e82ed826683 100644
--- a/pkg/compiler/lib/src/diagnostics/messages.dart
+++ b/pkg/compiler/lib/src/diagnostics/messages.dart
@@ -1155,35 +1155,30 @@ void main() => new C().m(null);
 
       MessageKind.TYPE_VARIABLE_FROM_METHOD_NOT_REIFIED: const MessageTemplate(
           MessageKind.TYPE_VARIABLE_FROM_METHOD_NOT_REIFIED,
-          "Method type variables are not reified.",
-          howToFix: "Try using the intended upper bound of the "
-              "type variable, or dynamic."
-// TODO(eernst): These examples should be commented in with an `options:`
-// specifying "--generic-method-syntax" and made to work; moreover, the
-// compiler/dart2js test 'generic_method_type_usage' should be transformed to
-// similar examples of the relevant `MessageKind` entries.
-//
-//        examples: const [
-//            """
-// // Method type variables are not reified, so they cannot be returned.
-// Type f<T>() => T;
-//
-// main() => f<int>();
-// """,
-//            """
-// // Method type variables are not reified, so they cannot be tested dynamically.
-// bool f<T>(Object o) => o is T;
-//
-// main() => f<int>(42);
-// """,
-//            """
-// // Method type variables are not reified, so they cannot be tested dynamically.
-// bool f<T>(Object o) => o as T;
-//
-// main() => f<int>(42);
-// """
-//    ]
-      ),
+          "Method type variables do not have a runtime value.",
+          options: const ["--generic-method-syntax"],
+          howToFix: "Try using the upper bound of the type variable, "
+              "or refactor the code to avoid needing this runtime value.",
+          examples: const [
+            """
+// Method type variables are not reified, so they cannot be returned.
+Type f<T>() => T;
+
+main() => f<int>();
+""",
+            """
+// Method type variables are not reified, so they cannot be tested dynamically.
+bool f<T>(Object o) => o is T;
+
+main() => f<int>(42);
+""",
+            """
+// Method type variables are not reified, so they cannot be tested dynamically.
+bool f<T>(Object o) => o as T;
+
+main() => f<int>(42);
+"""
+          ]),
 
       MessageKind.INVALID_TYPE_VARIABLE_BOUND: const MessageTemplate(
           MessageKind.INVALID_TYPE_VARIABLE_BOUND,