add support hwc 1.1

Bug: 7124069

Change-Id: I53d705105c4ad8954d3f50ee4f4c8b7ec936b871
diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index 6785ba8..569f6bb 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -523,6 +523,10 @@
     }
 }
 
+bool Layer::isVisible() const {
+    return LayerBaseClient::isVisible() && (mActiveBuffer != NULL);
+}
+
 Region Layer::latchBuffer(bool& recomputeVisibleRegions)
 {
     ATRACE_CALL();