Extract DiagnosticReporter implementation from Compiler.

pkg/compiler/lib/src/helpers/helpers.dart

Index: pkg/compiler/lib/src/helpers/helpers.dart
diff --git a/pkg/compiler/lib/src/helpers/helpers.dart b/pkg/compiler/lib/src/helpers/helpers.dart
index 3a67978befe1666d4104f1f7910acc47bc3dea3f..6b3e787dfe591f01273ab105bc86b2953f97608f 100644
--- a/pkg/compiler/lib/src/helpers/helpers.dart
+++ b/pkg/compiler/lib/src/helpers/helpers.dart
@@ -15,6 +15,8 @@ import 'dart:convert';
 import '../../compiler.dart';
 import '../compiler.dart' show
     Compiler;
+import '../diagnostics/diagnostic_listener.dart' show
+    DiagnosticReporter;
 import '../diagnostics/invariant.dart' show
     DEBUG_MODE;
 import '../diagnostics/messages.dart' show
@@ -88,7 +90,9 @@ debugBreak() {
 }
 
 /// Function signature of [reportHere].
-typedef ReportHere(Compiler compiler, Spannable node, String debugMessage);
+typedef ReportHere(DiagnosticReporter reporter,
+                   Spannable node,
+                   String debugMessage);
 
 /// Print a message with a source location.
 ReportHere get reportHere {
@@ -97,8 +101,8 @@ ReportHere get reportHere {
 }
 
 /// Implementation of [reportHere]
-_reportHere(Compiler compiler, Spannable node, String debugMessage) {
-  compiler.reportInfo(node,
+_reportHere(DiagnosticReporter reporter, Spannable node, String debugMessage) {
+  reporter.reportInfo(node,
       MessageKind.GENERIC, {'text': 'HERE: $debugMessage'});
 }