Use file/offset/kind triplet as elements id.

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

Index: pkg/analysis_server/lib/src/services/index/store/memory_node_manager.dart
diff --git a/pkg/analysis_server/lib/src/services/index/store/memory_node_manager.dart b/pkg/analysis_server/lib/src/services/index/store/memory_node_manager.dart
index 27832d73839ce6f9ae76ce5204e013fe386b037a..500626bd8b6a5bfe3de575877efda68a30210935 100644
--- a/pkg/analysis_server/lib/src/services/index/store/memory_node_manager.dart
+++ b/pkg/analysis_server/lib/src/services/index/store/memory_node_manager.dart
@@ -12,9 +12,15 @@ import 'package:analysis_server/src/services/index/store/split_store.dart';
 import 'package:analyzer/src/generated/engine.dart';
 
 class MemoryNodeManager implements NodeManager {
-  StringCodec _stringCodec = new StringCodec();
-  ContextCodec _contextCodec = new ContextCodec();
-  ElementCodec _elementCodec;
+  @override
+  StringCodec stringCodec = new StringCodec();
+
+  @override
+  ContextCodec contextCodec = new ContextCodec();
+
+  @override
+  ElementCodec elementCodec;
+
   RelationshipCodec _relationshipCodec;
 
   int _locationCount = 0;
@@ -22,18 +28,8 @@ class MemoryNodeManager implements NodeManager {
   final Map<String, IndexNode> _nodes = new HashMap<String, IndexNode>();
 
   MemoryNodeManager() {
-    _elementCodec = new ElementCodec(_stringCodec);
-    _relationshipCodec = new RelationshipCodec(_stringCodec);
-  }
-
-  @override
-  ContextCodec get contextCodec {
-    return _contextCodec;
-  }
-
-  @override
-  ElementCodec get elementCodec {
-    return _elementCodec;
+    elementCodec = new ElementCodec(stringCodec);
+    _relationshipCodec = new RelationshipCodec(stringCodec);
   }
 
   @override
@@ -42,11 +38,6 @@ class MemoryNodeManager implements NodeManager {
   }
 
   @override
-  StringCodec get stringCodec {
-    return _stringCodec;
-  }
-
-  @override
   void clear() {
     _nodes.clear();
   }