Save and restore unified mode

ash/display/display_layout_store.cc

Index: ash/display/display_layout_store.cc
diff --git a/ash/display/display_layout_store.cc b/ash/display/display_layout_store.cc
index 466adbf4920b35c4f314cb77c7787d23e7524a58..c25bc0d66378c2986100af046695f73a499f154e 100644
--- a/ash/display/display_layout_store.cc
+++ b/ash/display/display_layout_store.cc
@@ -67,11 +67,13 @@ DisplayLayout DisplayLayoutStore::ComputeDisplayLayoutForDisplayIdPair(
           pair.first == layout.primary_id) ? layout : layout.Invert();
 }
 
-void DisplayLayoutStore::UpdateMirrorStatus(const DisplayIdPair& pair,
-                                            bool mirrored) {
+void DisplayLayoutStore::UpdateMultiDisplayState(const DisplayIdPair& pair,
+                                                 bool mirrored,
+                                                 bool default_unified) {
   if (paired_layouts_.find(pair) == paired_layouts_.end())
     CreateDisplayLayout(pair);
   paired_layouts_[pair].mirrored = mirrored;
+  paired_layouts_[pair].default_unified = default_unified;
 }
 
 void DisplayLayoutStore::UpdatePrimaryDisplayId(const DisplayIdPair& pair,