Use System.nanoTime() for timing measurements.

bramble-api/src/main/java/org/briarproject/bramble/util/TimeUtils.java

@@ -0,0 +1,14 @@
+package org.briarproject.bramble.util;
+
+public class TimeUtils {
+
+	private static final int NANOS_PER_MILLI = 1000 * 1000;
+
+	/**
+	 * Returns the elapsed time in milliseconds since some arbitrary
+	 * starting time. This is only useful for measuring elapsed time.
+	 */
+	public static long now() {
+		return System.nanoTime() / NANOS_PER_MILLI;
+	}
+}