Don't schedule indexing operations if index is null.

pkg/analysis_server/lib/src/operation/operation_analysis.dart

Index: pkg/analysis_server/lib/src/operation/operation_analysis.dart
diff --git a/pkg/analysis_server/lib/src/operation/operation_analysis.dart b/pkg/analysis_server/lib/src/operation/operation_analysis.dart
index 51725f7a7d448e8968fb5a5eebb1c73d58b301d3..e5f5edb17f12b987371667db400549f456144cad 100644
--- a/pkg/analysis_server/lib/src/operation/operation_analysis.dart
+++ b/pkg/analysis_server/lib/src/operation/operation_analysis.dart
@@ -24,7 +24,9 @@ import 'package:analyzer/src/generated/source.dart';
  */
 void scheduleIndexOperation(AnalysisServer server, String file,
     AnalysisContext context, CompilationUnit dartUnit) {
-  server.addOperation(new _DartIndexOperation(context, file, dartUnit));
+  if (server.index != null) {
+    server.addOperation(new _DartIndexOperation(context, file, dartUnit));
+  }
 }
 
 /**
@@ -236,8 +238,7 @@ class PerformAnalysisOperation extends ServerOperation {
   }
 
   void _updateIndex(AnalysisServer server, List<ChangeNotice> notices) {
-    Index index = server.index;
-    if (index == null) {
+    if (server.index == null) {
       return;
     }
     for (ChangeNotice notice in notices) {