Populate initial base info with unknown state values

Set the current state key to a HashableDimensionKey with -1
(kStateUnknown) for each sliced state atom. Previously, the current
state key was being set to the DEFAULT_DIMENSION_KEY which is an empty
HashableDimensionKey.

Bug: 155487198
Test: make statsd_test && adb sync data && adb shell
data/nativetest/statsd_test/statsd_test

Change-Id: Icaa187ecae599407695d86eec6104d210aa98714