Prepare for decoupling analyzer ASTs from element model.

pkg/analysis_server/lib/src/services/completion/dart/completion_manager.dart

Index: pkg/analysis_server/lib/src/services/completion/dart/completion_manager.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/completion_manager.dart b/pkg/analysis_server/lib/src/services/completion/dart/completion_manager.dart
index 26a9af5c403832e3a88932ff2ccc955f2848742a..847b281cc9abf416c480081cc46d3a78021a6d51 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/completion_manager.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/completion_manager.dart
@@ -19,6 +19,7 @@ import 'package:analysis_server/src/services/completion/dart/contribution_sorter
 import 'package:analysis_server/src/services/completion/dart/optype.dart';
 import 'package:analysis_server/src/services/search/search_engine.dart';
 import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/standard_resolution_map.dart';
 import 'package:analyzer/dart/ast/standard_ast_factory.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/element.dart';
@@ -179,7 +180,8 @@ class DartCompletionRequestImpl implements DartCompletionRequest {
   @override
   LibraryElement get coreLib {
     if (result != null) {
-      AnalysisContext context = result.unit.element.context;
+      AnalysisContext context =
+          resolutionMap.elementForCompilationUnit(result.unit).context;
       _coreLib = context.typeProvider.objectType.element.library;
     } else {
       Source coreUri = sourceFactory.forUri('dart:core');
@@ -325,7 +327,8 @@ class DartCompletionRequestImpl implements DartCompletionRequest {
       return _resolvedUnits;
     }
     if (result != null) {
-      _resolvedUnits = result.unit.element.library.units;
+      _resolvedUnits =
+          resolutionMap.elementForCompilationUnit(result.unit).library.units;
       return _resolvedUnits;
     }
     LibraryElement libElem = libraryElement;
@@ -396,7 +399,7 @@ class DartCompletionRequestImpl implements DartCompletionRequest {
     if (request.context == null) {
       unit = request.result.unit;
       // TODO(scheglov) support for parts
-      libSource = unit.element.source;
+      libSource = resolutionMap.elementForCompilationUnit(unit).source;
     } else {
       Source source = request.source;
       AnalysisContext context = request.context;