[Power] Prevent override of power level locked with Web API

[Power] Prevent override of power level locked with Web API

Chromium used to override power level locked by Web API with its own
settings. The level set by Web API was not restored.
From now on, Chromium will not override power level lock, after receiving
"__DisableChromiumInternalPowerLock" message from the Web API
and will be able to control the locked power level,
after receiving "__EnableChromiumInternalPowerLock" message.

Change-Id: Ia14f873766e26bd02ae7eecb182c69e0b6af00e8
Signed-off-by: Pawel Wasowski <p.wasowski2@partner.samsung.com>