Add interfaces for a new compiler API.

pkg/compiler/lib/src/old_to_new_api.dart

+// Copyright (c) 2015, 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.
+
+/// Implementation of the new compiler API in '../compiler_new.dart' through the
+/// old compiler API in '../compiler.dart'.
+
+library compiler.api.legacy;
+
+import 'dart:async' show EventSink, Future;
+import 'null_compiler_output.dart' show NullSink;
+import '../compiler.dart';
+import '../compiler_new.dart';
+
+/// Implementation of [CompilerInput] using a [CompilerInputProvider].
+class LegacyCompilerInput implements CompilerInput {
+  final CompilerInputProvider _inputProvider;
+
+  LegacyCompilerInput(this._inputProvider);
+
+  @override
+  Future readFromUri(Uri uri) {
+    return _inputProvider(uri);
+  }
+}
+
+/// Implementation of [CompilerDiagnostics] using a [DiagnosticHandler].
+class LegacyCompilerDiagnostics implements CompilerDiagnostics {
+  final DiagnosticHandler _handler;
+
+  LegacyCompilerDiagnostics(this._handler);
+
+  @override
+  void report(Uri uri, int begin, int end,
+                        String message, Diagnostic kind) {
+    _handler(uri, begin, end, message, kind);
+  }
+}
+
+/// Implementation of [CompilerOutput] using an optional
+/// [CompilerOutputProvider].
+class LegacyCompilerOutput implements CompilerOutput {
+  final CompilerOutputProvider _outputProvider;
+
+  LegacyCompilerOutput([this._outputProvider]);
+
+  @override
+  EventSink<String> createEventSink(String name, String extension) {
+    if (_outputProvider != null) return _outputProvider(name, extension);
+    return NullSink.outputProvider(name, extension);
+  }
+}