Optimize top-level element declarations search.

pkg/analysis_server/lib/src/services/index/index.dart

Index: pkg/analysis_server/lib/src/services/index/index.dart
diff --git a/pkg/analysis_server/lib/src/services/index/index.dart b/pkg/analysis_server/lib/src/services/index/index.dart
index 6864e17c289c444a1edff8cab7f061df16d6537a..7cc6d251c8b5a2fad933fbae87d9ff0eb61778e5 100644
--- a/pkg/analysis_server/lib/src/services/index/index.dart
+++ b/pkg/analysis_server/lib/src/services/index/index.dart
@@ -14,6 +14,12 @@ import 'package:analyzer/src/generated/source.dart';
 
 
 /**
+ * A filter for [Element] names.
+ */
+typedef ElementNameFilter(String name);
+
+
+/**
  * The interface [Index] defines the behavior of objects that maintain an index
  * storing relations between [Element]s.
  *
@@ -50,6 +56,11 @@ abstract class Index {
       Relationship relationship);
 
   /**
+   * Returns top-level [Element]s whose names satisfy to [nameFilter].
+   */
+  List<Element> getTopDeclarations(ElementNameFilter nameFilter);
+
+  /**
    * Processes the given [HtmlUnit] in order to record the relationships.
    *
    * [context] - the [AnalysisContext] in which [HtmlUnit] was resolved.
@@ -357,20 +368,3 @@ class Relationship {
     return relationship;
   }
 }
-
-
-/**
- * An element to use when we want to request "defines" relations without
- * specifying an exact library.
- */
-class UniverseElement extends ElementImpl {
-  static final UniverseElement INSTANCE = new UniverseElement._();
-
-  UniverseElement._() : super("--universe--", -1);
-
-  @override
-  ElementKind get kind => ElementKind.UNIVERSE;
-
-  @override
-  accept(ElementVisitor visitor) => null;
-}