don't init ash window unless in ash mode

chrome/browser/ui/startup/startup_browser_creator_impl.cc

Index: chrome/browser/ui/startup/startup_browser_creator_impl.cc
diff --git a/chrome/browser/ui/startup/startup_browser_creator_impl.cc b/chrome/browser/ui/startup/startup_browser_creator_impl.cc
index 7434d9c7fff09403842d49496424ac332178f970..efdb84f868e66373ce3cdca9b0bd273d803bd4f2 100644
--- a/chrome/browser/ui/startup/startup_browser_creator_impl.cc
+++ b/chrome/browser/ui/startup/startup_browser_creator_impl.cc
@@ -810,15 +810,17 @@ Browser* StartupBrowserCreatorImpl::OpenTabsInBrowser(Browser* browser,
   }
 
 #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.