[Cronet] Add Hello World response to QuicTestServer and use it in bidirectional stream test.

components/cronet/ios/test/quic_test_server.h

Index: components/cronet/ios/test/quic_test_server.h
diff --git a/components/cronet/ios/test/quic_test_server.h b/components/cronet/ios/test/quic_test_server.h
index 2fae073a0c772bdfd8ba7e9faa6e575d5c1cbb5b..8b21cb280045c7f22440ab732e592dc73bdef4a6 100644
--- a/components/cronet/ios/test/quic_test_server.h
+++ b/components/cronet/ios/test/quic_test_server.h
@@ -11,6 +11,22 @@ bool StartQuicTestServer();
 
 void ShutdownQuicTestServer();
 
+extern const char kTestServerDomain[];
+extern const int kTestServerPort;
+extern const char kTestServerHost[];
+extern const char kTestServerUrl[];
+
+extern const char kStatusHeader[];
+
+extern const char kHelloBodyValue[];
+extern const char kHelloStatus[];
+
+extern const char kHelloHeaderName[];
+extern const char kHelloHeaderValue[];
+
+extern const char kHelloTrailerName[];
+extern const char kHelloTrailerValue[];
+
 }  // namespace cronet
 
 #endif  // COMPONENTS_CRONET_IOS_TEST_QUIC_TEST_SERVER_H_