Prepare for decoupling analyzer ASTs from element model.

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 0c4c85f8043f46490f8a71d307a538ffe5af0f2c..cea58f9d6ecd2ec712e2a09cf94ac7b24714439b 100644
--- a/pkg/analysis_server/lib/src/operation/operation_analysis.dart
+++ b/pkg/analysis_server/lib/src/operation/operation_analysis.dart
@@ -17,6 +17,7 @@ import 'package:analysis_server/src/protocol_server.dart' as protocol;
 import 'package:analysis_server/src/services/dependencies/library_dependencies.dart';
 import 'package:analysis_server/src/services/search/search_engine.dart';
 import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/resolution_accessors.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/src/generated/engine.dart';
@@ -71,7 +72,7 @@ scheduleImplementedNotification(
 void scheduleIndexOperation(
     AnalysisServer server, String file, CompilationUnit dartUnit) {
   if (server.index != null) {
-    AnalysisContext context = dartUnit.element.context;
+    AnalysisContext context = elementForCompilationUnit(dartUnit).context;
     server.addOperation(new _DartIndexOperation(context, file, dartUnit));
   }
 }