public boolean isProtobuf() {
        return is(PROTOBUF) || is(X_PROTOBUF)|| is(X_GOOGLE_PROTOBUF);
    }
Returns {@code true} when the subtype is one of {@link MediaType#PROTOBUF}, {@link MediaType#X_PROTOBUF}
and {@link MediaType#X_GOOGLE_PROTOBUF}. Otherwise {@code false}.

<pre>{@code
PROTOBUF.isProtobuf() // true
X_PROTOBUF.isProtobuf() // true
X_GOOGLE_PROTOBUF.isProtobuf() // true
}</pre>
core/src/main/java/com/linecorp/armeria/common/MediaType.java