dart2js: Move most of the code_emitter_task code into the program-builder.

tests/compiler/dart2js/deferred_not_in_main_test.dart

Index: tests/compiler/dart2js/deferred_not_in_main_test.dart
diff --git a/tests/compiler/dart2js/deferred_not_in_main_test.dart b/tests/compiler/dart2js/deferred_not_in_main_test.dart
index 9999881eff9678503476c6ca69bae2faab749f47..a4b8435fa599ea785c483952d48e5bab1207e60b 100644
--- a/tests/compiler/dart2js/deferred_not_in_main_test.dart
+++ b/tests/compiler/dart2js/deferred_not_in_main_test.dart
@@ -51,8 +51,6 @@ void main() {
     var foo1 = lib1.find("foo1");
     var foo2 = lib2.find("foo2");
 
-    var outputClassLists = backend.emitter.outputClassLists;
-
     Expect.notEquals(mainOutputUnit, outputUnitForElement(foo2));
   }));
 }