Add (an as yet unused) task

pkg/analyzer/lib/src/task/task_dart.dart

Index: pkg/analyzer/lib/src/task/task_dart.dart
diff --git a/pkg/analyzer/lib/src/task/task_dart.dart b/pkg/analyzer/lib/src/task/task_dart.dart
new file mode 100644
index 0000000000000000000000000000000000000000..8e123b3b8cfeb5701a6ca18c72a078117acd3096
--- /dev/null
+++ b/pkg/analyzer/lib/src/task/task_dart.dart
@@ -0,0 +1,86 @@
+// Copyright (c) 2014, 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.
+
+library engine.task.dart;
+
+import 'package:analyzer/src/generated/ast.dart';
+import 'package:analyzer/src/generated/element.dart';
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:analyzer/src/generated/resolver.dart';
+import 'package:analyzer/src/generated/source.dart';
+
+/**
+ * A `BuildUnitElementTask` builds a compilation unit element for a single
+ * compilation unit.
+ */
+class BuildUnitElementTask extends AnalysisTask {
+  /**
+   * The source for which an element model will be built.
+   */
+  final Source source;
+
+  /**
+   * The source of the library in which an element model will be built.
+   */
+  final Source library;
+
+  /**
+   * The compilation unit from which an element model will be built.
+   */
+  final CompilationUnit unit;
+
+  /**
+   * The element model that was built.
+   */
+  CompilationUnitElement unitElement;
+
+  /**
+   * Initialize a newly created task to build a compilation unit element for
+   * the given [source] in the given [library] based on the compilation [unit]
+   * that was parsed.
+   */
+  BuildUnitElementTask(InternalAnalysisContext context, this.source, this.library, this.unit)
+      : super(context);
+
+  @override
+  accept(AnalysisTaskVisitor visitor) {
+    return visitor.visitBuildUnitElementTask(this);
+  }
+
+  /**
+   * Return the compilation unit from which the element model was built.
+   */
+  CompilationUnit getCompilationUnit() {
+    return unit;
+  }
+
+  /**
+   * Return the source that is to be parsed.
+   */
+  Source getSource() {
+    return source;
+  }
+
+  /**
+   * Return the compilation unit element that was produced, or `null` if the
+   * task has not yet been performed or if an exception occurred.
+   */
+  CompilationUnitElement getUnitElement() {
+    return unitElement;
+  }
+
+  @override
+  void internalPerform() {
+    CompilationUnitBuilder builder = new CompilationUnitBuilder();
+    unitElement = builder.buildCompilationUnit(source, unit);
+  }
+
+  @override
+  String get taskDescription {
+    if (source == null) {
+      return "build the unit element model for null source";
+    }
+    return "build the unit element model for " + source.fullName;
+  }
+}