buffet: Add ability to add commands via buffet_client

Implemented "AddCommand" parameter in buffet_client that queues
a GCD command in buffet daemon.

BUG=chromium:412583
TEST=FEATURES=test emerge-link buffet

Change-Id: Ie5a6561efc8675ba5fb234c1151a0f1dbda39e5d
Reviewed-on: https://chromium-review.googlesource.com/217829
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Anton Muhin <antonm@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/buffet/manager.h b/buffet/manager.h
index 35a5534..be399d5 100644
--- a/buffet/manager.h
+++ b/buffet/manager.h
@@ -58,6 +58,9 @@
   // Handles calls to org.chromium.Buffet.Manager.UpdateState().
   void HandleUpdateState(chromeos::ErrorPtr* error,
                          const std::string& json_state_fragment);
+  // Handles calls to org.chromium.Buffet.Manager.AddCommand().
+  void HandleAddCommand(chromeos::ErrorPtr* error,
+                        const std::string& json_command);
   // Handles calls to org.chromium.Buffet.Manager.Test()
   std::string HandleTestMethod(chromeos::ErrorPtr* error,
                                const std::string& message);