BQ: Add and expose a unique id

Bug 29422927

Change-Id: I80eab94f073ebc378302f00fa86a740c3643657e
diff --git a/services/surfaceflinger/MonitoredProducer.h b/services/surfaceflinger/MonitoredProducer.h
index ce756dc..71b6b59 100644
--- a/services/surfaceflinger/MonitoredProducer.h
+++ b/services/surfaceflinger/MonitoredProducer.h
@@ -64,6 +64,7 @@
     virtual IBinder* onAsBinder();
     virtual status_t setSharedBufferMode(bool sharedBufferMode) override;
     virtual status_t setAutoRefresh(bool autoRefresh) override;
+    virtual status_t getUniqueId(uint64_t* outId) const override;
 
 private:
     sp<IGraphicBufferProducer> mProducer;