dart2js: Remove oldEmitter field in emitter-task.

tests/compiler/dart2js/mirrors_used_test.dart

Index: tests/compiler/dart2js/mirrors_used_test.dart
diff --git a/tests/compiler/dart2js/mirrors_used_test.dart b/tests/compiler/dart2js/mirrors_used_test.dart
index 3b2bb39012760b5a876c1ca4154405ddfdd5bb4f..53101cd5c5b2945870c38ce830db183f579b7bdc 100644
--- a/tests/compiler/dart2js/mirrors_used_test.dart
+++ b/tests/compiler/dart2js/mirrors_used_test.dart
@@ -89,10 +89,13 @@ void main() {
     expectedNames = expectedNames.map(backend.namer.asName).toList();
     expectedNames.addAll(nativeNames);
 
+    // Mirrors only work in the full emitter. We can thus be certain that the
+    // emitter is the full emitter.
+    OldEmitter fullEmitter = backend.emitter.emitter;
     Set recordedNames = new Set()
-        ..addAll(backend.emitter.oldEmitter.recordedMangledNames)
-        ..addAll(backend.emitter.oldEmitter.mangledFieldNames.keys)
-        ..addAll(backend.emitter.oldEmitter.mangledGlobalFieldNames.keys);
+        ..addAll(fullEmitter.recordedMangledNames)
+        ..addAll(fullEmitter.mangledFieldNames.keys)
+        ..addAll(fullEmitter.mangledGlobalFieldNames.keys);
     Expect.setEquals(new Set.from(expectedNames), recordedNames);
 
     for (var library in compiler.libraryLoader.libraries) {