Fix google-build-using-namespace
diff --git a/src/core/ext/filters/client_channel/http_connect_handshaker.cc b/src/core/ext/filters/client_channel/http_connect_handshaker.cc
index 1b9817c..979248e 100644
--- a/src/core/ext/filters/client_channel/http_connect_handshaker.cc
+++ b/src/core/ext/filters/client_channel/http_connect_handshaker.cc
@@ -382,8 +382,7 @@
 }  // namespace grpc_core
 
 void grpc_http_connect_register_handshaker_factory() {
-  using namespace grpc_core;
-  HandshakerRegistry::RegisterHandshakerFactory(
-      true /* at_start */, HANDSHAKER_CLIENT,
-      absl::make_unique<HttpConnectHandshakerFactory>());
+  grpc_core::HandshakerRegistry::RegisterHandshakerFactory(
+      true /* at_start */, grpc_core::HANDSHAKER_CLIENT,
+      absl::make_unique<grpc_core::HttpConnectHandshakerFactory>());
 }
diff --git a/src/core/lib/channel/handshaker.cc b/src/core/lib/channel/handshaker.cc
index 461a21d..8d1d45e 100644
--- a/src/core/lib/channel/handshaker.cc
+++ b/src/core/lib/channel/handshaker.cc
@@ -256,7 +256,7 @@
 void grpc_handshake_manager_add(grpc_handshake_manager* mgr,
                                 grpc_handshaker* handshaker) {
   // This is a transition method to aid the API change for handshakers.
-  using namespace grpc_core;
-  RefCountedPtr<Handshaker> refd_hs(static_cast<Handshaker*>(handshaker));
+  grpc_core::RefCountedPtr<grpc_core::Handshaker> refd_hs(
+      static_cast<grpc_core::Handshaker*>(handshaker));
   mgr->Add(refd_hs);
 }
diff --git a/test/core/handshake/readahead_handshaker_server_ssl.cc b/test/core/handshake/readahead_handshaker_server_ssl.cc
index c146850..708b316 100644
--- a/test/core/handshake/readahead_handshaker_server_ssl.cc
+++ b/test/core/handshake/readahead_handshaker_server_ssl.cc
@@ -77,11 +77,10 @@
 }  // namespace grpc_core
 
 int main(int /*argc*/, char* /*argv*/[]) {
-  using namespace grpc_core;
   grpc_init();
-  HandshakerRegistry::RegisterHandshakerFactory(
-      true /* at_start */, HANDSHAKER_SERVER,
-      absl::make_unique<ReadAheadHandshakerFactory>());
+  grpc_core::HandshakerRegistry::RegisterHandshakerFactory(
+      true /* at_start */, grpc_core::HANDSHAKER_SERVER,
+      absl::make_unique<grpc_core::ReadAheadHandshakerFactory>());
   const char* full_alpn_list[] = {"grpc-exp", "h2"};
   GPR_ASSERT(server_ssl_test(full_alpn_list, 2, "grpc-exp"));
   grpc_shutdown();