Split MessageKind into a MessageKind key and a MessageTemplate.

tests/compiler/dart2js/library_resolution_test.dart

Index: tests/compiler/dart2js/library_resolution_test.dart
diff --git a/tests/compiler/dart2js/library_resolution_test.dart b/tests/compiler/dart2js/library_resolution_test.dart
index ed41ebe3a3b25e16ed441e23165835c9b72fe7cd..5eeb342164e5e0fd216f0b919ba0e3b9b3144b5e 100644
--- a/tests/compiler/dart2js/library_resolution_test.dart
+++ b/tests/compiler/dart2js/library_resolution_test.dart
@@ -21,7 +21,8 @@ import 'package:compiler/src/elements/elements.dart' show
     LibraryElement;
 
 import 'package:compiler/src/dart2jslib.dart' show
-    MessageKind;
+    MessageKind,
+    MessageTemplate;
 
 import 'package:compiler/src/null_compiler_output.dart' show
     NullCompilerOutput;
@@ -92,7 +93,7 @@ main() {
   }
 
   String expectedMessage =
-      MessageKind.LIBRARY_NOT_FOUND.message(
+      MessageTemplate.TEMPLATES[MessageKind.LIBRARY_NOT_FOUND].message(
           {'resolvedUri': 'dart:mock2.dart'}).computeMessage();
 
   int actualMessageCount = 0;