dart2js: Remove oldEmitter field in emitter-task.

tests/compiler/dart2js/source_mapping_test.dart

Index: tests/compiler/dart2js/source_mapping_test.dart
diff --git a/tests/compiler/dart2js/source_mapping_test.dart b/tests/compiler/dart2js/source_mapping_test.dart
index a54caaca3b2bc87f5d7056ddba170975a5977e89..3b049471deb36b6c63d36ab23db33a7a60cd8de0 100644
--- a/tests/compiler/dart2js/source_mapping_test.dart
+++ b/tests/compiler/dart2js/source_mapping_test.dart
@@ -10,6 +10,7 @@ import 'package:compiler/src/io/source_file.dart';
 import 'package:compiler/src/io/source_information.dart';
 import "mock_compiler.dart";
 import 'package:compiler/src/js_backend/js_backend.dart';
+import 'package:compiler/src/js_emitter/js_emitter.dart';
 
 Future<CodeBuffer> compileAll(SourceFile sourceFile) {
   MockCompiler compiler = new MockCompiler.internal();
@@ -17,7 +18,10 @@ Future<CodeBuffer> compileAll(SourceFile sourceFile) {
   compiler.sourceFiles[uri.toString()] = sourceFile;
   JavaScriptBackend backend = compiler.backend;
   return compiler.runCompiler(uri).then((_) {
-    return backend.emitter.oldEmitter
+    // TODO(floitsch): the outputBuffers are only accessible in the full
+    // emitter.
+    OldEmitter fullEmitter = backend.emitter.emitter;
+    return fullEmitter
         .outputBuffers[compiler.deferredLoadTask.mainOutputUnit];
   });
 }