extract named constructor suggestions from prefixed element contributor

pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.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 analysis_server.src.provisional.completion.completion_dart;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/provisional/completion/completion_core.dart';
 import 'package:analysis_server/src/provisional/completion/dart/completion_target.dart';
 import 'package:analyzer/src/generated/ast.dart';
+import 'package:analyzer/src/generated/element.dart';
 
 export 'package:analysis_server/src/provisional/completion/completion_core.dart'
     show EMPTY_LIST;
 
 const int DART_RELEVANCE_COMMON_USAGE = 1200;
 const int DART_RELEVANCE_DEFAULT = 1000;
 const int DART_RELEVANCE_HIGH = 2000;
 const int DART_RELEVANCE_INHERITED_ACCESSOR = 1057;
 const int DART_RELEVANCE_INHERITED_FIELD = 1058;
 const int DART_RELEVANCE_INHERITED_METHOD = 1057;
@@ skipping 30 matching lines @@
       DartCompletionRequest request);
 }
 
 /**
  * The information about a requested list of completions within a Dart file.
  *
  * Clients may not extend, implement or mix-in this class.
  */
 abstract class DartCompletionRequest extends CompletionRequest {
   /**
+   * Return a [Future] that completes with the library element
+   * which contains the unit in which the completion is occurring.
+   * The [Future] may return `null` if the library cannot be determined
+   * (e.g. unlinked part file).
+   * Any information obtained from [target] prior to calling this method
+   * should be discarded as it may have changed.
+   */
+  Future<LibraryElement> get libraryElement;
+
+  /**
    * Return the completion target.  This determines what part of the parse tree
    * will receive the newly inserted text.
    */
   CompletionTarget get target;
 
   /**
    * Return a [Future] that completes with a compilation unit in which
    * all declarations in all scopes containing [target] have been resolved.
    * The [Future] may return `null` if the unit cannot be resolved
    * (e.g. unlinked part file).
    * Any information obtained from [target] prior to calling this method
    * should be discarded as it may have changed.
    */
   Future<CompilationUnit> resolveDeclarationsInScope();
 
   /**
    * Return a [Future] that completes when the element associated with
    * the given [identifier] is available or if the identifier cannot be resolved
    * (e.g. unknown identifier, completion aborted, etc).
    * Any information obtained from [target] prior to calling this method
    * should be discarded as it may have changed.
    */
   Future resolveIdentifier(SimpleIdentifier identifier);
 }