Fix a couple test timeouts.

test/server/utils.dart

Index: test/server/utils.dart
diff --git a/test/server/utils.dart b/test/server/utils.dart
index a4fd36af674b69f1e73a6091f2aad1505770cb96..75dc9b247a0f7363c27c50c39a54380b6b31407f 100644
--- a/test/server/utils.dart
+++ b/test/server/utils.dart
@@ -61,6 +61,20 @@ void expectErrorResponse(ServerController controller, request, int errorCode,
   })));
 }
 
+/// Returns a matcher that matches [Future]s that never complete.
+Matcher get doesNotComplete => predicate((future) {
+  future.then(expectAsync((_) {
+    // This will never be called. [expectAsync] with `count: 0` ensures that an
+    // error will be thrown when [future] completes.
+  }, count: 0));
+
+  // Make sure there's enough time in the test for [expectAsync] to fail if it's
+  // going to.
+  expect(pumpEventQueue(), completes);
+
+  return true;
+});
+
 /// Returns a matcher that matches a [json_rpc.RpcException] with an
 /// `invalid_params` error code.
 Matcher throwsInvalidParams(String message) {