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This is the preparation of the direct communication with tpm manager
daemon.

As patterns commonly adopted in other dbus clients, we also leave
`TestInterface` class for future extension.

To test the CL, a test-only CL is introduced to check if we can get TPM
status using the introduced classes.

BUG=b:172748724
TEST=build ok.
TEST=See above.

Change-Id: I94f2d37b4e03c0219e0463ad58bd05a581233a68
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2537731
Commit-Queue: Leo Lai <cylai@google.com>
Reviewed-by: Ryo Hashimoto <hashimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#829608}