Convert completion API to be future based

pkg/analysis_server/test/services/completion/completion_computer_test.dart

Index: pkg/analysis_server/test/services/completion/completion_computer_test.dart
diff --git a/pkg/analysis_server/test/services/completion/completion_computer_test.dart b/pkg/analysis_server/test/services/completion/completion_computer_test.dart
index 3e549ce9e8fec94bbd1ff07a0e506283756d4975..0cdeff95d1345abba213dfe8f826e560e21f3b05 100644
--- a/pkg/analysis_server/test/services/completion/completion_computer_test.dart
+++ b/pkg/analysis_server/test/services/completion/completion_computer_test.dart
@@ -90,11 +90,12 @@ class DartCompletionManagerTest extends AbstractSingleUnitTest {
     CompletionRequest completionRequest =
         new CompletionRequestImpl(server, context, source, 0);
     manager.results(completionRequest).listen((CompletionResult r) {
+      bool isLast = r is CompletionResultImpl ? r.isLast : true;
       switch (++count) {
         case 1:
           contributor1.assertCalls(context, source, 0, searchEngine);
           contributor2.assertCalls(context, source, 0, searchEngine);
-          expect(r.isLast, isFalse);
+          expect(isLast, isFalse);
           expect(r.suggestions, hasLength(1));
           expect(r.suggestions, contains(suggestion1));
           resolveLibrary();
@@ -102,7 +103,7 @@ class DartCompletionManagerTest extends AbstractSingleUnitTest {
         case 2:
           contributor1.assertFull(0);
           contributor2.assertFull(1);
-          expect(r.isLast, isTrue);
+          expect(isLast, isTrue);
           expect(r.suggestions, hasLength(2));
           expect(r.suggestions, contains(suggestion1));
           expect(r.suggestions, contains(suggestion2));
@@ -129,11 +130,12 @@ class DartCompletionManagerTest extends AbstractSingleUnitTest {
     CompletionRequest completionRequest =
         new CompletionRequestImpl(server, context, source, 0);
     manager.results(completionRequest).listen((CompletionResult r) {
+      bool isLast = r is CompletionResultImpl ? r.isLast : true;
       switch (++count) {
         case 1:
           contributor1.assertCalls(context, source, 0, searchEngine);
           contributor2.assertCalls(context, source, 0, searchEngine);
-          expect(r.isLast, isTrue);
+          expect(isLast, isTrue);
           expect(r.suggestions, hasLength(2));
           expect(r.suggestions, contains(suggestion1));
           expect(r.suggestions, contains(suggestion2));