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 f625ee55890c28979a57f901a4bc346485688cd7..ac7bb1a1458b54017ecc6182f0ae015d051f9274 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);
+
   void set_dont_warp_mouse(bool dont_warp_mouse) {
     dont_warp_mouse_ = dont_warp_mouse;
   }
@@ -100,6 +105,10 @@ 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_;
+
   // If true, the mouse pointer can't move from one display to another.
   bool dont_warp_mouse_;