Make monotonic_now a required parameter to PhasedLoop

This prepares us much better for mocking out time as part of the event
loop conversion.

Change-Id: I57560b97b265ddd41fe7a4e9f74d7b1324d15955
diff --git a/frc971/wpilib/sensor_reader.cc b/frc971/wpilib/sensor_reader.cc
index ec1e822..2e0cd0a 100644
--- a/frc971/wpilib/sensor_reader.cc
+++ b/frc971/wpilib/sensor_reader.cc
@@ -100,7 +100,7 @@
     LOG(INFO, "Defaulting to open loop pwm synchronization\n");
   }
   ::aos::time::PhasedLoop phased_loop(
-      period,
+      period, ::aos::monotonic_clock::now(),
       pwm_trigger_ ? ::std::chrono::milliseconds(3) : chrono::milliseconds(4));
 
   ::aos::SetCurrentThreadRealtimePriority(40);