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

ash/display/display_controller.h

Index: ash/display/display_controller.h
diff --git a/ash/display/display_controller.h b/ash/display/display_controller.h
index 7a151fbfe1a0c12f72c40805f5a06e2265ef1512..47b3cef59b382c8710110909aae7c28b15c61610 100644
--- a/ash/display/display_controller.h
+++ b/ash/display/display_controller.h
@@ -68,6 +68,11 @@ class ASH_EXPORT DisplayController : public aura::DisplayObserver {
   }
   void SetSecondaryDisplayLayout(SecondaryDisplayLayout layout);
 
+  int secondary_display_offset() const {
+    return secondary_display_offset_;
+  }
+  void SetSecondaryDisplayOffset(int offset);
+
   // Warps the mouse cursor to an alternate root window when the
   // |point_in_root|, which is the location of the mouse cursor,
   // hits or exceeds the edge of the |root_window| and the mouse cursor
@@ -96,6 +101,10 @@ class ASH_EXPORT DisplayController : public aura::DisplayObserver {
 
   SecondaryDisplayLayout secondary_display_layout_;
 
+  // The offset of the position of the secondary display.  The offset is
+  // based on the top/left edge of the primary display.
+  int secondary_display_offset_;
+
   DISALLOW_COPY_AND_ASSIGN(DisplayController);
 };