Make backend and reporter customizable.

pkg/compiler/lib/src/common/backend_api.dart

Index: pkg/compiler/lib/src/common/backend_api.dart
diff --git a/pkg/compiler/lib/src/common/backend_api.dart b/pkg/compiler/lib/src/common/backend_api.dart
index 7949d099a026c2bb43f5762ec87775c2ca7e5eef..6b809e9967ffa50fb189e8aa751fa3d975cef1a6 100644
--- a/pkg/compiler/lib/src/common/backend_api.dart
+++ b/pkg/compiler/lib/src/common/backend_api.dart
@@ -24,7 +24,7 @@ import '../elements/elements.dart'
         LibraryElement,
         MetadataAnnotation,
         MethodElement;
-import '../enqueue.dart' show Enqueuer, ResolutionEnqueuer;
+import '../enqueue.dart' show Enqueuer, EnqueueTask, CodegenEnqueuer, ResolutionEnqueuer;
 import '../io/code_output.dart' show CodeBuffer;
 import '../io/source_information.dart' show SourceInformationStrategy;
 import '../js_backend/backend_helpers.dart' as js_backend show BackendHelpers;
@@ -38,10 +38,14 @@ import '../serialization/serialization.dart'
 import '../tree/tree.dart' show Node, Send;
 import '../universe/call_structure.dart' show CallStructure;
 import '../universe/world_impact.dart' show ImpactStrategy, WorldImpact;
-import 'codegen.dart' show CodegenWorkItem;
-import 'registry.dart' show Registry;
-import 'tasks.dart' show CompilerTask;
-import 'work.dart' show ItemCompilationContext;
+import 'codegen.dart' show
+    CodegenWorkItem;
+import 'registry.dart' show
+    Registry;
+import 'tasks.dart' show
+    CompilerTask;
+import 'work.dart' show
+    ItemCompilationContext;
 
 abstract class Backend {
   final Compiler compiler;
@@ -398,6 +402,8 @@ abstract class Backend {
 
   /// Backend access to the front-end.
   Frontend get frontend => compiler.resolution;
+
+  EnqueueTask makeEnqueuer() => new EnqueueTask(compiler);
 }
 
 /// Interface for resolving calls to foreign functions.