Make subclasses of AbstractContextTest asynchronous.

pkg/analysis_server/test/abstract_context.dart

Index: pkg/analysis_server/test/abstract_context.dart
diff --git a/pkg/analysis_server/test/abstract_context.dart b/pkg/analysis_server/test/abstract_context.dart
index ac7d8c0cfb8015a99db98f4ec894d5356c8e1e1f..ed9bb2f48e18b7a6f1d132e62a6a39cb9f61cd49 100644
--- a/pkg/analysis_server/test/abstract_context.dart
+++ b/pkg/analysis_server/test/abstract_context.dart
@@ -4,6 +4,8 @@
 
 library testing.abstract_context;
 
+import 'dart:async';
+
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/visitor.dart';
@@ -123,12 +125,12 @@ class AbstractContextTest {
     AnalysisEngine.instance.processRequiredPlugins();
   }
 
-  CompilationUnit resolveDartUnit(Source unitSource, Source librarySource) {
-    return context.resolveCompilationUnit2(unitSource, librarySource);
-  }
-
-  CompilationUnit resolveLibraryUnit(Source source) {
-    return context.resolveCompilationUnit2(source, source);
+  Future<CompilationUnit> resolveLibraryUnit(Source source) async {
+    if (enableNewAnalysisDriver) {
+      return (await driver.getResult(source.fullName))?.unit;
+    } else {
+      return context.resolveCompilationUnit2(source, source);
+    }
   }
 
   void setUp() {