Extract DiagnosticReporter implementation from Compiler.

tests/compiler/dart2js/analyze_unused_dart2js_test.dart

Index: tests/compiler/dart2js/analyze_unused_dart2js_test.dart
diff --git a/tests/compiler/dart2js/analyze_unused_dart2js_test.dart b/tests/compiler/dart2js/analyze_unused_dart2js_test.dart
index 0c4870bafee3a1bf871d09d504865c9083a8d9b2..581b25bdd847b661c2219d6e4424f02394b42c6e 100644
--- a/tests/compiler/dart2js/analyze_unused_dart2js_test.dart
+++ b/tests/compiler/dart2js/analyze_unused_dart2js_test.dart
@@ -86,23 +86,23 @@ bool checkResults(Compiler compiler, CollectingDiagnosticHandler handler) {
   void checkLive(member) {
     if (member.isFunction) {
       if (compiler.enqueuer.resolution.hasBeenResolved(member)) {
-        compiler.reportHint(compiler.createMessage(
+        compiler.reporter.reportHintMessage(
             member, MessageKind.GENERIC,
-            {'text': "Helper function in production code '$member'."}));
+            {'text': "Helper function in production code '$member'."});
       }
     } else if (member.isClass) {
       if (member.isResolved) {
-        compiler.reportHint(compiler.createMessage(
+        compiler.reporter.reportHintMessage(
             member, MessageKind.GENERIC,
-            {'text': "Helper class in production code '$member'."}));
+            {'text': "Helper class in production code '$member'."});
       } else {
         member.forEachLocalMember(checkLive);
       }
     } else if (member.isTypedef) {
       if (member.isResolved) {
-        compiler.reportHint(compiler.createMessage(
+        compiler.reporter.reportHintMessage(
             member, MessageKind.GENERIC,
-            {'text': "Helper typedef in production code '$member'."}));
+            {'text': "Helper typedef in production code '$member'."});
       }
     }
   }