fix test cases

Author: AgraVator

cronet/src/test/java/io/grpc/cronet/CronetClientTransportTest.java

@@ -34,6 +34,7 @@
 import io.grpc.Status;
 import io.grpc.cronet.CronetChannelBuilder.StreamBuilderFactory;
 import io.grpc.internal.ClientStreamListener;
+import io.grpc.internal.DisconnectError
 import io.grpc.internal.GrpcAttributes;
 import io.grpc.internal.ManagedClientTransport;
 import io.grpc.internal.TransportTracer;