BQ: Add and expose a unique id

Bug 29422927

Change-Id: I80eab94f073ebc378302f00fa86a740c3643657e
diff --git a/services/surfaceflinger/MonitoredProducer.cpp b/services/surfaceflinger/MonitoredProducer.cpp
index faab62c..fd33d5c 100644
--- a/services/surfaceflinger/MonitoredProducer.cpp
+++ b/services/surfaceflinger/MonitoredProducer.cpp
@@ -149,6 +149,10 @@
             outTransformMatrix);
 }
 
+status_t MonitoredProducer::getUniqueId(uint64_t* outId) const {
+    return mProducer->getUniqueId(outId);
+}
+
 IBinder* MonitoredProducer::onAsBinder() {
     return IInterface::asBinder(mProducer).get();
 }