use propogated type for completions

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

 // Copyright (c) 2014, 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.computer.dart.invocation;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/services/completion/dart_completion_manager.dart';
 import 'package:analysis_server/src/services/completion/optype.dart';
@@ skipping 126 matching lines @@
       node = node.parent;
     }
     if (node is ConstructorName) {
       // some PrefixedIdentifier nodes are transformed into
       // ConstructorName nodes during the resolution process.
       return new NamedConstructorSuggestionBuilder(request).computeFull(node);
     }
     if (node is PrefixedIdentifier) {
       SimpleIdentifier prefix = node.prefix;
       if (prefix != null) {
-        Element element = prefix.bestElement;
-        if (element != null) {
-          return element.accept(this);
+        if (prefix.propagatedType != null) {
+          InterfaceTypeSuggestionBuilder.suggestionsFor(
+              request,
+              prefix.propagatedType);
+        } else {
+          Element element = prefix.bestElement;
+          if (element != null) {
+            return element.accept(this);
+          }
         }
       }
     }
     return new Future.value(false);
   }
 
   @override
   Future<bool> visitClassElement(ClassElement element) {
     if (element != null) {
       InterfaceType type = element.type;
@@ skipping 46 matching lines @@
     }
     return new Future.value(false);
   }
 
   @override
   Future<bool> visitVariableElement(VariableElement element) {
     InterfaceTypeSuggestionBuilder.suggestionsFor(request, element.type);
     return new Future.value(true);
   }
 }