Handshaker plugin mechanism.
diff --git a/BUILD b/BUILD
index 74de1fe..3122dc0 100644
--- a/BUILD
+++ b/BUILD
@@ -421,6 +421,8 @@
         "src/core/lib/channel/connected_channel.c",
         "src/core/lib/channel/deadline_filter.c",
         "src/core/lib/channel/handshaker.c",
+        "src/core/lib/channel/handshaker_factory.c",
+        "src/core/lib/channel/handshaker_registry.c",
         "src/core/lib/channel/http_client_filter.c",
         "src/core/lib/channel/http_server_filter.c",
         "src/core/lib/channel/message_size_filter.c",
@@ -536,6 +538,8 @@
         "src/core/lib/channel/context.h",
         "src/core/lib/channel/deadline_filter.h",
         "src/core/lib/channel/handshaker.h",
+        "src/core/lib/channel/handshaker_factory.h",
+        "src/core/lib/channel/handshaker_registry.h",
         "src/core/lib/channel/http_client_filter.h",
         "src/core/lib/channel/http_server_filter.h",
         "src/core/lib/channel/message_size_filter.h",