Fix batterystat Counter misreporting when charging

The BatteryStatsImpl.Counter would previously increment the count even
when the timeBase was off. Then, when the timeBase was turned back on,
the count would be decreased back to the correct value. Thus, when the
timeBase was on, the reported count would be correct, but when the
timeBase was off, the reported count would be wrong (too high). Here, we
fix this.
We also make some other minor improvements.

Bug: 36728346
Test: runtest -x frameworks/base/core/tests/coretests/src/com/android/internal/os/BatteryStatsTests.java
Change-Id: I2fa566a8a4cad4cdff0e6caef37b1eef36a3f5c4