Add one field (sampling_rate_denom) in NetworkDnsEventReported

The sample rate of DNS stats(to statsd) is 1/sampling_rate_denom.

Bug: 119862317
Test: ./out/host/linux-x86/bin/statsd_testdrive 116
Merged-In: Ifd496f01ceaeb48de0361280c2315c3733c24f66
Merged-In: If142d8a764437e6a349b122b241c72d069071846
(cherry picked from commit 71b457e4e13ae130fceeec45f19c8430c938e172)

Change-Id: Ic1cdc849e024d4c3c220914a0a62316dd2566748
2 files changed