Make *Time explicitly nanoseconds duration for OS X.

Signed-off-by: Harvey Tuch <[email protected]>

Author: htuch

include/envoy/common/time.h

@@ -11,8 +11,8 @@ namespace Envoy {
  * SystemTime should be used when getting a time to present to the user, e.g. for logging.
  * MonotonicTime should be used when tracking time for computing an interval.
  */
-typedef std::chrono::time_point<std::chrono::system_clock> SystemTime;
-typedef std::chrono::time_point<std::chrono::steady_clock> MonotonicTime;
+typedef std::chrono::time_point<std::chrono::system_clock, std::chrono::nanoseconds> SystemTime;
+typedef std::chrono::time_point<std::chrono::steady_clock, std::chrono::nanoseconds> MonotonicTime;
 
 /**
  * Abstraction for getting the current system time. Useful for testing.