Create a task in the new task model to compute constant dependencies.

pkg/analyzer/lib/task/dart.dart

Index: pkg/analyzer/lib/task/dart.dart
diff --git a/pkg/analyzer/lib/task/dart.dart b/pkg/analyzer/lib/task/dart.dart
index 7356c97f9dc60f1756105d1bc4432186f69ccc88..c99d95098120fe1a45642d8497a93084aa4ba0b0 100644
--- a/pkg/analyzer/lib/task/dart.dart
+++ b/pkg/analyzer/lib/task/dart.dart
@@ -14,6 +14,16 @@ import 'package:analyzer/src/task/dart.dart';
 import 'package:analyzer/task/model.dart';
 
 /**
+ * The list of [Element]s which a given constant element depends on.
+ *
+ * The result is only available for targets representing a constant [Element]
+ * (i.e. a constant variable declaration, a constant constructor, or a
+ * parameter element with a default value).
+ */
+final ListResultDescriptor<Element> CONSTANT_DEPENDENCIES =
+    new ListResultDescriptor<Element>('CONSTANT_DEPENDENCIES', <Element>[]);
+
+/**
  * The analysis errors associated with a target.
  *
  * The result is only available for targets representing a Dart compilation unit.