Add utilities to support the outline notification

pkg/analyzer_plugin/lib/plugin/outline_mixin.dart

Index: pkg/analyzer_plugin/lib/plugin/outline_mixin.dart
diff --git a/pkg/analyzer_plugin/lib/plugin/outline_mixin.dart b/pkg/analyzer_plugin/lib/plugin/outline_mixin.dart
new file mode 100644
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+++ b/pkg/analyzer_plugin/lib/plugin/outline_mixin.dart
@@ -0,0 +1,68 @@
+// Copyright (c) 2017, 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.
+
+import 'dart:async';
+
+import 'package:analyzer/dart/analysis/results.dart';
+import 'package:analyzer/src/dart/analysis/driver.dart';
+import 'package:analyzer_plugin/plugin/plugin.dart';
+import 'package:analyzer_plugin/protocol/protocol.dart';
+import 'package:analyzer_plugin/src/utilities/outline/outline.dart';
+import 'package:analyzer_plugin/utilities/generator.dart';
+import 'package:analyzer_plugin/utilities/outline/outline.dart';
+
+/**
+ * A mixin that can be used when creating a subclass of [ServerPlugin] and
+ * mixing in [OutlineMixin]. This implements the creation of the outline
+ * request based on the assumption that the driver being created is an
+ * [AnalysisDriver].
+ *
+ * Clients may not extend or implement this class, but are allowed to use it as
+ * a mix-in when creating a subclass of [ServerPlugin] that also uses
+ * [OutlineMixin] as a mix-in.
+ */
+abstract class DartOutlineMixin implements OutlineMixin {
+  @override
+  Future<OutlineRequest> getOutlineRequest(String path) async {
+    ResolveResult result = await getResolveResult(path);
+    return new DartOutlineRequestImpl(resourceProvider, result);
+  }
+}
+
+/**
+ * A mixin that can be used when creating a subclass of [ServerPlugin] to
+ * provide most of the implementation for producing outline notifications.
+ *
+ * Clients may not extend or implement this class, but are allowed to use it as
+ * a mix-in when creating a subclass of [ServerPlugin].
+ */
+abstract class OutlineMixin implements ServerPlugin {
+  /**
+   * Return a list containing the outline contributors that should be used to
+   * create outline information for the file with the given [path].
+   */
+  List<OutlineContributor> getOutlineContributors(String path);
+
+  /**
+   * Return the outline request that should be passes to the contributors
+   * returned from [getOutlineContributors].
+   *
+   * Throw a [RequestFailure] if the request could not be created.
+   */
+  Future<OutlineRequest> getOutlineRequest(String path);
+
+  @override
+  Future<Null> sendOutlineNotification(String path) async {
+    try {
+      OutlineRequest request = await getOutlineRequest(path);
+      OutlineGenerator generator =
+          new OutlineGenerator(getOutlineContributors(path));
+      GeneratorResult generatorResult =
+          await generator.generateOutlineNotification(request);
+      generatorResult.sendNotifications(channel);
+    } on RequestFailure {
+      // If we couldn't analyze the file, then don't send a notification.
+    }
+  }
+}