extract named constructor suggestions from prefixed element contributor

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

 // 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 services.completion.dart.manager;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/provisional/completion/completion_core.dart'
     show CompletionContributor, CompletionRequest;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/provisional/completion/dart/completion_plugin.dart';
 import 'package:analysis_server/src/provisional/completion/dart/completion_target.dart';
 import 'package:analysis_server/src/services/completion/completion_core.dart';
 import 'package:analysis_server/src/services/search/search_engine.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/context/context.dart'
     show AnalysisFutureHelper, AnalysisContextImpl;
 import 'package:analyzer/src/generated/ast.dart';
+import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart' hide AnalysisContextImpl;
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/task/dart.dart';
 import 'package:analyzer/task/dart.dart';
 
 /**
  * [DartCompletionManager] determines if a completion request is Dart specific
  * and forwards those requests to all [DartCompletionContributor]s.
  */
 class DartCompletionManager implements CompletionContributor {
@@ skipping 52 matching lines @@
 
   DartCompletionRequestImpl._(
       AnalysisContext context,
       ResourceProvider resourceProvider,
       SearchEngine searchEngine,
       Source source,
       int offset)
       : super(context, resourceProvider, searchEngine, source, offset);
 
   @override
+  Future<LibraryElement> get libraryElement async {
+    //TODO(danrubel) build the library element rather than all the declarations
+    CompilationUnit unit = await resolveDeclarationsInScope();
+    if (unit != null) {
+      CompilationUnitElement elem = unit.element;
+      if (elem != null) {
+        return elem.library;
+      }
+    }
+    return null;
+  }
+
+  @override
   CompletionTarget get target {
     if (_target == null) {
       CompilationUnit unit = context.computeResult(source, PARSED_UNIT);
       _target = new CompletionTarget.forOffset(unit, offset);
     }
     return _target;
   }
 
   @override
   Future<CompilationUnit> resolveDeclarationsInScope() async {
@@ skipping 73 matching lines @@
     // Gracefully degrade if unit cannot be resolved
     if (resolvedUnit == null) {
       return;
     }
 
     // Recompute the target for the newly resolved unit
     _target = new CompletionTarget.forOffset(resolvedUnit, offset);
     _haveResolveDeclarationsInScope = true;
   }
 }