[Cherry-pick] Cache timestamps in mProtoOut.

Remove separate vector used for caching timestamps and cache the
timestamps directly in mProtoOut while maintaining ShellData proto
structure.

Bug: 274610336
Test: m
Test: statsd_test
Test: libstatspull_test
Test: CtsStatsdHostTestCases:android.cts.statsd.subscriber.ShellSubscriberTest
Merged-In: I081f00fed0a3c26ffe48472ce60884db6778964f
Change-Id: I081f00fed0a3c26ffe48472ce60884db6778964f
(cherry picked from commit 36f603fcfea322082977b31dbc69956f235b8ed5)
2 files changed