don't init ash window unless in ash mode

chrome/browser/ui/startup/startup_browser_creator_impl.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/ui/startup/startup_browser_creator_impl.h"
 
 #include <algorithm>
 #include <vector>
 
 #include "base/bind.h"
@@ skipping 792 matching lines @@
   } else {
 #if defined(TOOLKIT_GTK)
     // Setting the time of the last action on the window here allows us to steal
     // focus, which is what the user wants when opening a new tab in an existing
     // browser window.
     gtk_util::SetWMLastUserActionTime(browser->window()->GetNativeWindow());
 #endif
   }
 
 #if defined(USE_ASH)
-  // Set the browser's root window to be an active root window now so
-  // that that web contents can determine correct scale factor for the
-  // renderer. This is a short term fix for crbug.com/155201.  Without
-  // this, the renderer may use wrong scale factor first, then
-  // switched to the correct scale factor, which can cause race
-  // condition and lead to the results rendered at wrong scale factor.
-  // Long term fix is tracked in crbug.com/15543.
-  ash::Shell::GetInstance()->set_active_root_window(
-      browser->window()->GetNativeWindow()->GetRootWindow());
+  if (ash::Shell::HasInstance()) {
+    // Set the browser's root window to be an active root window now so
+    // that that web contents can determine correct scale factor for the
+    // renderer. This is a short term fix for crbug.com/155201.  Without
+    // this, the renderer may use wrong scale factor first, then
+    // switched to the correct scale factor, which can cause race
+    // condition and lead to the results rendered at wrong scale factor.
+    // Long term fix is tracked in crbug.com/15543.
+    ash::Shell::GetInstance()->set_active_root_window(
+        browser->window()->GetNativeWindow()->GetRootWindow());
+  }
 #endif
 
   // In kiosk mode, we want to always be fullscreen, so switch to that now.
   if (CommandLine::ForCurrentProcess()->HasSwitch(switches::kKioskMode))
     chrome::ToggleFullscreenMode(browser);
 
   bool first_tab = true;
   for (size_t i = 0; i < tabs.size(); ++i) {
     // We skip URLs that we'd have to launch an external protocol handler for.
     // This avoids us getting into an infinite loop asking ourselves to open
@@ skipping 198 matching lines @@
         // New:
         prefs->GetString(prefs::kHomePage),
         prefs->GetBoolean(prefs::kHomePageIsNewTabPage),
         prefs->GetBoolean(prefs::kShowHomeButton),
         // Backup:
         backup_homepage,
         backup_homepage_is_ntp,
         backup_show_home_button));
   }
 }