Chrome Version: 61.0.3163.100 (Official Build) (64-bit) (cohort: Stable)
OS: Win/Mac/Linux

What steps will reproduce the problem?
When same audio devices are plugged into the system, client will see same device names. When device change happens, for example, one of the devices are removed/added, client is not able identify which device is actually changed, so it cannot make the right decision to switch audio playback to the appropriate device.

What is the expected result?
PPB_DeviceRef_Shared has the ability to return device uid stored in |DeviceRefData::id|, so we only need to add a new method
|PPB_DeviceRef_Dev::GetId()|, and implement it through |PPB_DeviceRef_Shared::GetId()|-> |DeviceRefData::id|

What happens instead?
When same output devices are connected to the system, switching audio output among those devices will be messed up.