SF: replicate mSidebandStream in LayerBE

Add a copy of mSidebandStream in LayerBE.  This is
one of the few data items that is replicated in
both FE and BE.

Test: build
Change-Id: Ief98645a4fa178e2606c0c337b3f260a1766597a
diff --git a/services/surfaceflinger/Layer.h b/services/surfaceflinger/Layer.h
index 5dfc963..b5638e0 100644
--- a/services/surfaceflinger/Layer.h
+++ b/services/surfaceflinger/Layer.h
@@ -73,6 +73,8 @@
 public:
     LayerBE();
 
+    sp<NativeHandle> mSidebandStream;
+
     // The mesh used to draw the layer in GLES composition mode
     Mesh mMesh;