refactor optype to be computed once per refactoring request

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_ast_visitor.dart';
+import 'package:analysis_server/src/services/completion/optype.dart';
 import 'package:analysis_server/src/services/completion/suggestion_builder.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
-import 'package:analyzer/src/generated/scanner.dart';
 
 import '../../protocol_server.dart' show CompletionSuggestionKind;
 
 /**
  * A computer for calculating invocation / access suggestions
  * `completion.getSuggestions` request results.
  */
 class InvocationComputer extends DartCompletionComputer {
   SuggestionBuilder builder;
 
   @override
   bool computeFast(DartCompletionRequest request) {
-
-    // Determine the type of suggestions to be made
-    OpTypeAstVisitor opTypeVisitor = new OpTypeAstVisitor(request.offset);
-    request.node.accept(opTypeVisitor);
-
-    // Build the suggestions
-    if (opTypeVisitor.includeInvocationSuggestions) {
+    OpType optype = request.optype;
+    if (optype.includeInvocationSuggestions) {
       builder = request.node.accept(new _InvocationAstVisitor(request));
       if (builder != null) {
         return builder.computeFast(request.node);
       }
     }
 
     return true;
   }
 
   @override
@@ skipping 178 matching lines @@
 
   @override
   Future<bool> visitVariableElement(VariableElement element) {
     DartType type = element.type;
     if (type != null) {
       ClassElementSuggestionBuilder.suggestionsFor(request, type.element);
     }
     return new Future.value(true);
   }
 }