refactor optype to be computed once per refactoring request

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

Index: pkg/analysis_server/lib/src/services/completion/invocation_computer.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/invocation_computer.dart b/pkg/analysis_server/lib/src/services/completion/invocation_computer.dart
index b7d2c64e49524989e84c3e3e683e32c898d1eda6..348021e44d0aa382381cd3dd05af5fdb8040cb64 100644
--- a/pkg/analysis_server/lib/src/services/completion/invocation_computer.dart
+++ b/pkg/analysis_server/lib/src/services/completion/invocation_computer.dart
@@ -7,11 +7,10 @@ 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;
 
@@ -24,13 +23,8 @@ class InvocationComputer extends DartCompletionComputer {
 
   @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);