Create renderers for ExtensionHosts one a time to avoid blocking the UI.

chrome/browser/cocoa/extension_view_mac.mm

 // Copyright (c) 2009 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/cocoa/extension_view_mac.h"
 
 #include "chrome/browser/extensions/extension_host.h"
 #include "chrome/browser/renderer_host/render_view_host.h"
 #include "chrome/browser/renderer_host/render_widget_host_view_mac.h"
 
@@ skipping 46 matching lines @@
 
 void ExtensionViewMac::CreateWidgetHostView() {
   DCHECK(!render_widget_host_view_);
   render_widget_host_view_ = new RenderWidgetHostViewMac(render_view_host());
 
   // The RenderWidgetHostViewMac is owned by its native view, which is created
   // in an autoreleased state. retain it, so that it doesn't immediately
   // disappear.
   [render_widget_host_view_->native_view() retain];
 
-  extension_host_->CreateRenderView(render_widget_host_view_);
+  extension_host_->CreateRenderViewSoon(render_widget_host_view_);
 }