Add API for contributing to the index

pkg/analysis_server/lib/analysis/index/index_dart.dart

Index: pkg/analysis_server/lib/analysis/index/index_dart.dart
diff --git a/pkg/analysis_server/lib/analysis/index/index_dart.dart b/pkg/analysis_server/lib/analysis/index/index_dart.dart
new file mode 100644
index 0000000000000000000000000000000000000000..511c7eedafa617c7174a4b49588f0312998210f9
--- /dev/null
+++ b/pkg/analysis_server/lib/analysis/index/index_dart.dart
@@ -0,0 +1,41 @@
+// Copyright (c) 2015, 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 analysis_server.analysis.index.index_core;
+
+import 'package:analysis_server/analysis/index/index_core.dart';
+import 'package:analyzer/src/generated/ast.dart';
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:analyzer/src/generated/source.dart';
+
+/**
+ * An [IndexContributor] that can be used to contribute relationships for Dart
+ * files.
+ *
+ * Clients are expected to subtype this class when implementing plugins.
+ */
+abstract class DartIndexContributor extends IndexContributor {
+  @override
+  void contributeTo(IndexStore store, AnalysisContext context, Source source) {
+    if (!AnalysisEngine.isDartFileName(source.fullName)) {
+      return;
+    }
+    List<Source> libraries = context.getLibrariesContaining(source);
+    if (libraries.isEmpty) {
+      return;
+    }
+    libraries.forEach((Source library) {
+      CompilationUnit unit = context.resolveCompilationUnit2(source, library);
+      if (unit != null) {
+        internalContributeTo(store, unit);
+      }
+    });
+  }
+
+  /**
+   * Contribute relationships to the given index [store] based on the given
+   * fully resolved compilation[unit].
+   */
+  void internalContributeTo(IndexStore store, CompilationUnit unit);
+}