Extract DiagnosticReporter implementation from Compiler.

pkg/compiler/lib/src/js_emitter/startup_emitter/emitter.dart

Index: pkg/compiler/lib/src/js_emitter/startup_emitter/emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/startup_emitter/emitter.dart b/pkg/compiler/lib/src/js_emitter/startup_emitter/emitter.dart
index 45ccabec333803cb213a711624fab6e834fef86b..ea0537a16e735b457d3ce2d54f5d5c450eacb965 100644
--- a/pkg/compiler/lib/src/js_emitter/startup_emitter/emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/startup_emitter/emitter.dart
@@ -27,6 +27,9 @@ import '../js_emitter.dart' show
 import '../js_emitter.dart' as emitterTask show
     Emitter;
 
+import '../../diagnostics/diagnostic_listener.dart' show
+    DiagnosticReporter;
+
 import '../../diagnostics/spannable.dart' show
     NO_LOCATION_SPANNABLE;
 
@@ -44,6 +47,8 @@ class Emitter implements emitterTask.Emitter {
         _emitter = new ModelEmitter(
             compiler, namer, nativeEmitter, shouldGenerateSourceMap);
 
+  DiagnosticReporter get reporter => _compiler.reporter;
+
   @override
   String get patchVersion => "startup";
 
@@ -184,7 +189,7 @@ class Emitter implements emitterTask.Emitter {
         return js.js.expressionTemplateFor("$functionAccess(#)");
 
       default:
-        _compiler.internalError(NO_LOCATION_SPANNABLE,
+        reporter.internalError(NO_LOCATION_SPANNABLE,
             "Unhandled Builtin: $builtin");
         return null;
     }