HostTiming: Pause the hardware clock on pause.

src/common/wall_clock.cpp

@@ -53,6 +53,10 @@ public:
         return Common::Divide128On32(temporary, 1000000000).first;
     }
 
+    void Pause(bool is_paused) override {
+        // Do nothing in this clock type.
+    }
+
 private:
     base_time_point start_time;
 };