Make AssistContributor 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 46f0dbf2a027bd5a94111d50925e2e9c2f4aea90..80498906924e085d80ebbe5ba320627935ba336d 100644
--- a/pkg/analysis_server/test/abstract_context.dart
+++ b/pkg/analysis_server/test/abstract_context.dart
@@ -10,6 +10,7 @@ import 'package:analyzer/source/package_map_resolver.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart';
+import 'package:analyzer/src/generated/java_engine.dart' show CaughtException;
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer/src/generated/source_io.dart';
 
@@ -91,6 +92,7 @@ class AbstractContextTest {
     context = AnalysisEngine.instance.createAnalysisContext();
     context.sourceFactory =
         new SourceFactory([SDK_RESOLVER, packageResolver, resourceResolver]);
+    AnalysisEngine.instance.logger = PrintLogger.instance;
   }
 
   void setupResourceProvider() {
@@ -100,6 +102,46 @@ class AbstractContextTest {
   void tearDown() {
     context = null;
     provider = null;
+    AnalysisEngine.instance.logger = null;
+  }
+}
+
+/**
+ * Instances of the class [PrintLogger] print all of the errors.
+ */
+class PrintLogger implements Logger {
+  static final Logger instance = new PrintLogger();
+
+  @override
+  void logError(String message, [CaughtException exception]) {
+    print(message);
+    if (exception != null) {
+      print(exception);
+    }
+  }
+
+  @override
+  void logError2(String message, Object exception) {
+    print(message);
+    if (exception != null) {
+      print(exception);
+    }
+  }
+
+  @override
+  void logInformation(String message, [CaughtException exception]) {
+    print(message);
+    if (exception != null) {
+      print(exception);
+    }
+  }
+
+  @override
+  void logInformation2(String message, Object exception) {
+    print(message);
+    if (exception != null) {
+      print(exception);
+    }
   }
 }