code: public java.lang.String getMethodName() {
      java.lang.Object ref = methodName_;
      if (ref instanceof java.lang.String) {
        return (java.lang.String) ref;
      } else {
        com.google.protobuf.ByteString bs = 
            (com.google.protobuf.ByteString) ref;
        java.lang.String s = bs.toStringUtf8();
        methodName_ = s;
        return s;
      }
    }
docs: <pre>
  Extensible method_name information enabling third-party users to mark a
  SignatureDef as supporting a particular method. This enables producers and
  consumers of SignatureDefs, e.g. a model definition library and a serving
  library to have a clear hand-off regarding the semantics of a computation.
  Note that multiple SignatureDefs in a single MetaGraphDef may have the same
  method_name. This is commonly used to support multi-headed computation,
  where a single graph computation may return multiple results.
  </pre>
  
  <code>optional string method_name = 3;</code>