[ Merge of http://go/wvgerrit/120510 ]
* Added some comments to clarify which clock times are computed at the
client and at the provisioning service. More detail is present in the
device_files.proto
* Moved helper methods |SetDeviceCertificate| and
|ExtractFromDeviceCertificate| from class methods to anonymous
namespace
* Removed some commented out code
Bug: 169740403
Test: WV unit/integration
Change-Id: Ic263f3dfe296fff6d9b5380b2e7c663d87022cb2
f6b4d140f4