Add BatteryUsageStats.add(BatteryUsageStats)

Bug: 187223764
Test: atest FrameworksCoreTests:com.android.internal.os.BatteryUsageStatsTest
Change-Id: I1e5060d726fd0f4634fd658483e80a9ab02e24fb
Merged-In: I1e5060d726fd0f4634fd658483e80a9ab02e24fb
(cherry picked from commit 63d9aecdbbd2ac03b31daa481819e9fd57428630)
5 files changed