Allow offset for secondary display position in chrome://settings/display.

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index e6e5ef9b36df7be5f53fb6729951a4724c00e5b9..92dc37a2032617db0f8177fe45726d27fab4f777 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -737,6 +737,10 @@ const char kEnableCrosDRM[] = "settings.privacy.drm_enabled";
 //  3 - The secondary display is at the left of the primary display.
 // TODO(mukai,oshima): update the format of the multi-display settings.
 const char kSecondaryDisplayLayout[] = "settings.display.secondary_layout";
+
+// An integer pref that specifies how far the secondary display is positioned
+// from the edge of the primary display.
+const char kSecondaryDisplayOffset[] = "settings.display.secondary_offset";
 #endif  // defined(OS_CHROMEOS)
 
 // The disabled messages in IPC logging.