Don't store empty objects on SF traces

Proto3 doesn't store default values for object, however, it stored the
object start-end tags if an empty object was created.

Do not create objects when they are empty

Test: Flash a device. Record SF trace. Open them in the new winscope
version with "display defaults" unchecked. Check if there are no empty
objects

Change-Id: I3f48047e43e9c62c572d5b83e63a0f96527ef146
diff --git a/services/surfaceflinger/layerproto/layers.proto b/services/surfaceflinger/layerproto/layers.proto
index faf0c54..a0fb0a0 100644
--- a/services/surfaceflinger/layerproto/layers.proto
+++ b/services/surfaceflinger/layerproto/layers.proto
@@ -113,6 +113,7 @@
   float dtdx = 2;
   float dsdy = 3;
   float dtdy = 4;
+  int32 type = 5;
 }
 
 message RegionProto {