Magnifier border is now more visible on light backgrounds.

ash/display/window_tree_host_manager.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/display/window_tree_host_manager.h"
 
 #include <algorithm>
 #include <cmath>
 #include <map>
 #include <memory>
@@ skipping 566 matching lines @@
     AshWindowTreeHost* ash_host =
         AddWindowTreeHostForDisplay(display, AshWindowTreeHostInitParams());
     RootWindowController::CreateForSecondaryDisplay(ash_host);
 
     // Magnifier controllers keep pointers to the current root window.
     // Update them here to avoid accessing them later.
     Shell::GetInstance()->magnification_controller()->SwitchTargetRootWindow(
         ash_host->AsWindowTreeHost()->window(), false);
     Shell::GetInstance()
         ->partial_magnification_controller()
-        ->SwitchTargetRootWindow(ash_host->AsWindowTreeHost()->window());
+        ->SwitchTargetRootWindowIfNeeded(
+            ash_host->AsWindowTreeHost()->window());
 
     AshWindowTreeHost* to_delete = primary_tree_host_for_replace_;
     primary_tree_host_for_replace_ = nullptr;
 
     // Show the shelf if the original WTH had a visible system
     // tray. It may or may not be visible depending on OOBE state.
     ash::SystemTray* old_tray =
         GetRootWindowController(to_delete->AsWindowTreeHost()->window())
             ->GetSystemTray();
     ash::SystemTray* new_tray =
@@ skipping 247 matching lines @@
   SetDisplayPropertiesOnHost(ash_host, display);
 
 #if defined(OS_CHROMEOS)
   if (switches::ConstrainPointerToRoot())
     ash_host->ConfineCursorToRootWindow();
 #endif
   return ash_host;
 }
 
 }  // namespace ash