public final boolean notifyMessageChannelReady(Bundle extras) {
        mMessageChannelCreated = true;
        return notifyMessageChannelReadyInternal(extras);
    }
Records that the message channel has been created and calls through to {@link
#notifyMessageChannelReadyInternal}, which will notify the service if it's connected.
@param extras Unused.
@return Whether the notification was sent successfully.
customtabs/src/android/support/customtabs/PostMessageServiceConnection.java