[HatoholArmPluginTestPair] Use a reference object to call a virtual method.
[HatoholArmPluginBase] Prepare a mechanism to synchronize on an unexpected initiation.

HatoholArmPlugin offers synchronization APIs that are  assumed to
typically be used from another thread. When an unexcpected initiation
happens the another thread sometimes needs to synchornize with the
HatoholArmPluginBase's thread. This patch enables the feature for that.