Deprecate 'singleton' option in chrome.apps.window.create().

chrome/browser/extensions/api/app_window/app_window_api.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 "chrome/browser/extensions/api/app_window/app_window_api.h"
 
 #include "apps/app_window_contents.h"
 #include "apps/shell_window.h"
 #include "apps/shell_window_registry.h"
 #include "apps/ui/native_app_window.h"
@@ skipping 141 matching lines @@
     if (options->id.get()) {
       // TODO(mek): use URL if no id specified?
       // Limit length of id to 256 characters.
       if (options->id->length() > 256) {
         error_ = app_window_constants::kInvalidWindowId;
         return false;
       }
 
       create_params.window_key = *options->id;
 
+      if (options->singleton && *options->singleton == false) {
+        WriteToConsole(
+          content::CONSOLE_MESSAGE_LEVEL_WARNING,
+          "The 'singleton' option in chrome.apps.window.create() is deprecated!"
+          " Change your code to no longer rely on this.");
+      }
+
       if (!options->singleton || *options->singleton) {
         ShellWindow* window = apps::ShellWindowRegistry::Get(
             GetProfile())->GetShellWindowForAppAndKey(extension_id(),
                                                       create_params.window_key);
         if (window) {
           content::RenderViewHost* created_view =
               window->web_contents()->GetRenderViewHost();
           int view_id = MSG_ROUTING_NONE;
           if (render_view_host_->GetProcess()->GetID() ==
               created_view->GetProcess()->GetID()) {
@@ skipping 141 matching lines @@
           ->HadDevToolsAttached(created_view)) {
     new DevToolsRestorer(this, created_view);
     return true;
   }
 
   SendResponse(true);
   return true;
 }
 
 }  // namespace extensions