Add proxy mapper hook.
diff --git a/binding.gyp b/binding.gyp
index 479403e..dd6db14 100644
--- a/binding.gyp
+++ b/binding.gyp
@@ -773,6 +773,8 @@
         'src/core/ext/client_channel/lb_policy_factory.c',
         'src/core/ext/client_channel/lb_policy_registry.c',
         'src/core/ext/client_channel/parse_address.c',
+        'src/core/ext/client_channel/proxy_mapper.c',
+        'src/core/ext/client_channel/proxy_mapper_registry.c',
         'src/core/ext/client_channel/resolver.c',
         'src/core/ext/client_channel/resolver_factory.c',
         'src/core/ext/client_channel/resolver_registry.c',