Fix moving the mouse between two displays after the secondary display becomes primary.

ash/display/extended_mouse_warp_controller.cc

Index: ash/display/extended_mouse_warp_controller.cc
diff --git a/ash/display/extended_mouse_warp_controller.cc b/ash/display/extended_mouse_warp_controller.cc
index 8d044637b91f67dcbd7fd421bff48944cbe86f6e..e1846c540fc2b86b179f07b100ffb5704b05ad0f 100644
--- a/ash/display/extended_mouse_warp_controller.cc
+++ b/ash/display/extended_mouse_warp_controller.cc
@@ -88,18 +88,21 @@ ExtendedMouseWarpController::ExtendedMouseWarpController(
                     drag_source != nullptr);
     }
   } else {
+    // Make sure to set |a| as the primary display, and |b| as the secondary
+    // display. DisplayLayout::Position is defined in terms of primary.
     DisplayLayout::Position position =
         display_manager->GetCurrentDisplayLayout().position;
-    const gfx::Display& a = display_manager->GetDisplayAt(0);
-    const gfx::Display& b = display_manager->GetDisplayAt(1);
+    const gfx::Display& a = Shell::GetScreen()->GetPrimaryDisplay();
+    const gfx::Display& b = ScreenUtil::GetSecondaryDisplay();
 
     // TODO(oshima): Use ComputeBondary instead.
-    if (position == DisplayLayout::TOP || position == DisplayLayout::BOTTOM)
+    if (position == DisplayLayout::TOP || position == DisplayLayout::BOTTOM) {
       AddWarpRegion(CreateHorizontalEdgeBounds(a, b, position),
                     drag_source != nullptr);
-    else
+    } else {
       AddWarpRegion(CreateVerticalEdgeBounds(a, b, position),
                     drag_source != nullptr);
+    }
   }
 }
 
@@ -148,8 +151,8 @@ void ExtendedMouseWarpController::SetEnabled(bool enabled) {
 
 void ExtendedMouseWarpController::AddWarpRegion(
     scoped_ptr<WarpRegion> warp_region,
-    bool drag_source) {
-  if (drag_source) {
+    bool has_drag_source) {
+  if (has_drag_source) {
     warp_region->shared_display_edge_indicator.reset(
         new SharedDisplayEdgeIndicator);
     warp_region->shared_display_edge_indicator->Show(