Save and restore unified mode

ash/display/display_layout_store.h

Index: ash/display/display_layout_store.h
diff --git a/ash/display/display_layout_store.h b/ash/display/display_layout_store.h
index a9675371269867c1f2e354522c4680cb21f1c1dc..6841ea906aa5f8057d0f6b408be2cde03a1a49d1 100644
--- a/ash/display/display_layout_store.h
+++ b/ash/display/display_layout_store.h
@@ -37,11 +37,12 @@ class ASH_EXPORT DisplayLayoutStore {
   DisplayLayout ComputeDisplayLayoutForDisplayIdPair(
       const DisplayIdPair& display_pair);
 
-  // Update the mirrored flag in the display layout for
+  // Update the multi display state in the display layout for
   // |display_pair|.  This creates new display layout if no layout is
   // registered for |display_pair|.
-  void UpdateMirrorStatus(const DisplayIdPair& display_pair,
-                          bool mirrored);
+  void UpdateMultiDisplayState(const DisplayIdPair& display_pair,
+                               bool mirrored,
+                               bool default_unified);
 
   // Update the |primary_id| in the display layout for
   // |display_pair|.  This creates new display layout if no layout is