Stats log interface for single node attribution chain.

Usually the input parameters for attribution chain is list of int64/string.
The new c++interface takes one int64 and one string as input and write
as a single node into logd.

This will help avoid allocating temp objects in battery stats java code.

Test: all statsd unit test passed.
Change-Id: Ia0f7f26b71a570bd3628c42726a5afb0a500d073