Add utilities to support the outline notification

pkg/analyzer_plugin/lib/src/utilities/outline/outline.dart

Index: pkg/analyzer_plugin/lib/src/utilities/outline/outline.dart
diff --git a/pkg/analyzer_plugin/lib/src/utilities/outline/outline.dart b/pkg/analyzer_plugin/lib/src/utilities/outline/outline.dart
new file mode 100644
index 0000000000000000000000000000000000000000..3329e16fcd476766ee733f456dc35248365b7f1e
--- /dev/null
+++ b/pkg/analyzer_plugin/lib/src/utilities/outline/outline.dart
@@ -0,0 +1,65 @@
+// 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 'package:analyzer/dart/analysis/results.dart';
+import 'package:analyzer/file_system/file_system.dart';
+import 'package:analyzer_plugin/protocol/protocol_common.dart'
+    hide AnalysisError;
+import 'package:analyzer_plugin/utilities/outline/outline.dart';
+
+/**
+ * A concrete implementation of [DartOutlineRequest].
+ */
+class DartOutlineRequestImpl implements DartOutlineRequest {
+  @override
+  final ResourceProvider resourceProvider;
+
+  @override
+  final ResolveResult result;
+
+  /**
+   * Initialize a newly create request with the given data.
+   */
+  DartOutlineRequestImpl(this.resourceProvider, this.result);
+
+  @override
+  String get path => result.path;
+}
+
+/**
+ * A concrete implementation of [OutlineCollector].
+ */
+class OutlineCollectorImpl implements OutlineCollector {
+  /**
+   * A list containing the top-level outline nodes.
+   */
+  List<Outline> outlines = <Outline>[];
+
+  /**
+   * A stack keeping track of the outline nodes that have been started but not
+   * yet ended.
+   */
+  List<Outline> outlineStack = <Outline>[];
+
+  @override
+  void endElement() {
+    outlineStack.removeLast();
+  }
+
+  @override
+  void startElement(Element element, int offset, int length) {
+    Outline outline = new Outline(element, offset, length);
+    if (outlineStack.isEmpty) {
+      outlines.add(outline);
+    } else {
+      List<Outline> children = outlineStack.last.children;
+      if (children == null) {
+        children = <Outline>[];
+        outlineStack.last.children = children;
+      }
+      children.add(outline);
+    }
+    outlineStack.add(outline);
+  }
+}