buffet: Add base.updateBaseConfiguration implementation

Required base command handled by buffet.

BUG=brillo:810
TEST=`FEATURES=test emerge-gizmo buffet`

Change-Id: I97ecd9f5d792cc636e76bbff92899a7ddfa4a605
Reviewed-on: https://chromium-review.googlesource.com/273618
Reviewed-by: Vitaly Buka <vitalybuka@chromium.org>
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
Tested-by: Vitaly Buka <vitalybuka@chromium.org>
diff --git a/buffet/states/state_manager.h b/buffet/states/state_manager.h
index cf2c60a..a34f7c1 100644
--- a/buffet/states/state_manager.h
+++ b/buffet/states/state_manager.h
@@ -61,6 +61,7 @@
   std::vector<StateChange> GetAndClearRecordedStateChanges();
 
  private:
+  friend class BaseApiHandlerTest;
   friend class StateManagerTest;
 
   // Updates a single property value. |full_property_name| must be the full