Build API: Added method discovery service.

Added simple method discovery service.
Fixed contrib/gen_call_scripts.

BUG=chromium:978441
TEST=manual, run_tests

Change-Id: I8ce2b2f8fcdf03265210a509087d3af06567c910
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1675738
Reviewed-by: Alex Klein <saklein@chromium.org>
Commit-Queue: Alex Klein <saklein@chromium.org>
Tested-by: Alex Klein <saklein@chromium.org>
Auto-Submit: Alex Klein <saklein@chromium.org>
diff --git a/api/router.py b/api/router.py
index e51eade..56127c3 100644
--- a/api/router.py
+++ b/api/router.py
@@ -20,6 +20,7 @@
 
 from chromite.api import controller
 from chromite.api import field_handler
+from chromite.api.gen.chromite.api import api_pb2
 from chromite.api.gen.chromite.api import artifacts_pb2
 from chromite.api.gen.chromite.api import binhost_pb2
 from chromite.api.gen.chromite.api import build_api_pb2
@@ -332,6 +333,7 @@
   Args:
     router (Router): The router.
   """
+  router.Register(api_pb2)
   router.Register(artifacts_pb2)
   router.Register(binhost_pb2)
   router.Register(depgraph_pb2)