Introduce chrome.enterprise.reportingPrivate.getDeviceInfo() API.

This is a private API for getting the device state for enterprise reporting.
This CL uses a stub implementation for now. Platform-specific implementations
will be added in future CLs.

TEST=manual + unit test with stub
BUG=996079

Change-Id: I2bb1d6035c11dea530058582b51835197b8da462
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1846754
Commit-Queue: Tim Song <[email protected]>
Reviewed-by: Karan Bhatia <[email protected]>
Reviewed-by: Gustavo Sacomoto <[email protected]>
Reviewed-by: Owen Min <[email protected]>
Cr-Commit-Position: refs/heads/master@{#721854}
9 files changed