Add extra logging for lock contention

When we get contention which is longer than kLongWaitMs (= 100ms) we
log to logcat.

Example output:
W/art     ( 9960): Long monitor contention event with owner method=void com.android.server.am.BroadcastQueue.processNextBroadcast(boolean) from BroadcastQueue.java:542 waiters=1 for 243ms

Bug: 17787391
Change-Id: Id1f92d9c41ec909d221871ecc2ff6181dcec2ed4