Make backend and reporter customizable.

pkg/compiler/lib/src/apiimpl.dart

Index: pkg/compiler/lib/src/apiimpl.dart
diff --git a/pkg/compiler/lib/src/apiimpl.dart b/pkg/compiler/lib/src/apiimpl.dart
index 3046dfd417db49155111fb3239d09551dfe77325..7a76e2b9aa25cd55085067e868a81cccf8998d9b 100644
--- a/pkg/compiler/lib/src/apiimpl.dart
+++ b/pkg/compiler/lib/src/apiimpl.dart
@@ -16,6 +16,8 @@ import 'package:package_config/src/util.dart' show checkValidPackageUri;
 import '../compiler_new.dart' as api;
 import 'common/tasks.dart' show GenericTask;
 import 'common.dart';
+import 'common/backend_api.dart' show
+    Backend;
 import 'compiler.dart';
 import 'diagnostics/messages.dart' show Message;
 import 'elements/elements.dart' as elements;
@@ -46,12 +48,14 @@ class CompilerImpl extends Compiler {
   Uri get libraryRoot => options.platformConfigUri.resolve(".");
 
   CompilerImpl(this.provider, api.CompilerOutput outputProvider, this.handler,
-      CompilerOptions options)
+      CompilerOptions options,
+      {MakeBackendFuncion makeBackend, MakeReporterFunction makeReporter})
       : resolvedUriTranslator = new ForwardingResolvedUriTranslator(),
         super(
             options: options,
             outputProvider: outputProvider,
-            environment: new _Environment(options.environment)) {
+            environment: new _Environment(options.environment),
+            makeBackend: makeBackend, makeReporter: makeReporter) {
     _Environment env = environment;
     env.compiler = this;
     tasks.addAll([