Use ScopedUtfChars (fixes a leak in TrafficStats, and fixes a crash in Wifi in
a case where GetStringChars could have been called with a pending exception).
Change-Id: I3465ff392b4038dfdafa6af80ec1314cc6d6a11c
Also change phone's ConnectionStateTrackers to use it directly,
rather than through the INetStat binder interface.
Bug: 2578938
Change-Id: I8858e2609cbec3be845a0ce5178cb03f67e01b41