Looper: use pthread_once for TLS key initialization.

Also fix a Valgrind complaint by zeroing out the entire epoll event
struct since otherwise the data field union would be partly
uninitialized (but not in a harmful way).

Change-Id: I2091ce517e87fcad7c9caf90e2c5e4854a7ca465
diff --git a/include/utils/Looper.h b/include/utils/Looper.h
index 7d90866..3f00b78 100644
--- a/include/utils/Looper.h
+++ b/include/utils/Looper.h
@@ -205,6 +205,7 @@
 
     int pollInner(int timeoutMillis);
 
+    static void initTLSKey();
     static void threadDestructor(void *st);
 };