dart2js: fix try/poi after refactor

pkg/dart2js_incremental/lib/caching_compiler.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart2js_incremental;
 
 /// Do not call this method directly. It will be made private.
 // TODO(ahe): Make this method private.
 Future<Compiler> reuseCompiler(
     {CompilerDiagnostics diagnosticHandler,
@@ skipping 167 matching lines @@
 
   void close() {
     if (data != null) {
       onClose(data.join());
       data = null;
     }
   }
 }
 
 /// Output provider which collect output in [output].
-class OutputProvider {
+class OutputProvider implements CompilerOutput {
   final Map<String, String> output = new Map<String, String>();
 
-  EventSink<String> call(String name, String extension) {
+  EventSink<String> createEventSink(String name, String extension) {
     return new StringEventSink((String data) {
       output['$name.$extension'] = data;
     });
   }
 
   String operator[] (String key) => output[key];
 }