[ONOS-7989] add sync button on roadm GUI view.

Change-Id: I0f27ac6c9c100f54180c490fc043da65ef1225e0
diff --git a/apps/roadm/src/main/java/org/onosproject/roadm/RoadmService.java b/apps/roadm/src/main/java/org/onosproject/roadm/RoadmService.java
index 4cd5fcf2..c9e65d8 100644
--- a/apps/roadm/src/main/java/org/onosproject/roadm/RoadmService.java
+++ b/apps/roadm/src/main/java/org/onosproject/roadm/RoadmService.java
@@ -93,7 +93,7 @@
     void setTargetPortPower(DeviceId deviceId, PortNumber portNumber, long power);
 
     /**
-     * Returns the target power for a port if the port has configurable target power.
+     * Returns the target power stored in storage for a port if the port has configurable target power.
      *
      * @param deviceId DeviceId of the device to configure
      * @param portNumber PortNumber of the port to configure
@@ -102,6 +102,14 @@
     Long getTargetPortPower(DeviceId deviceId, PortNumber portNumber);
 
     /**
+     * Sync-up the target power for a port if the operator want to check the configuration.
+     * @param deviceId DeviceId of the device to configure
+     * @param portNumber PortNumber of the port to configure
+     * @return the target power if the port has a target power, null otherwise
+     */
+    Long syncTargetPortPower(DeviceId deviceId, PortNumber portNumber);
+
+    /**
      * Sets the attenuation of a connection. This does not check that attenuation
      * is within the acceptable range.
      *