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

chrome/browser/extensions/extension_host.h

Index: chrome/browser/extensions/extension_host.h
diff --git a/chrome/browser/extensions/extension_host.h b/chrome/browser/extensions/extension_host.h
index 3b3d64ef7503661a375189e26e49f9a76729e7a4..617cd8e71937dbd6a05cf265d88dc43602d73484 100644
--- a/chrome/browser/extensions/extension_host.h
+++ b/chrome/browser/extensions/extension_host.h
@@ -38,6 +38,8 @@ class ExtensionHost : public RenderViewHostDelegate,
                       public ExtensionFunctionDispatcher::Delegate,
                       public NotificationObserver {
  public:
+  class ProcessCreationQueue;
+
   // Enable DOM automation in created render view hosts.
   static void EnableDOMAutomation() { enable_dom_automation_ = true; }
 
@@ -75,10 +77,10 @@ class ExtensionHost : public RenderViewHostDelegate,
   // Returns true if the render view is initialized and didn't crash.
   bool IsRenderViewLive() const;
 
-  // Initializes our RenderViewHost by creating its RenderView and navigating
-  // to this host's url.  Uses host_view for the RenderViewHost's view (can be
-  // NULL).
-  void CreateRenderView(RenderWidgetHostView* host_view);
+  // Prepares to initializes our RenderViewHost by creating its RenderView and
+  // navigating to this host's url. Uses host_view for the RenderViewHost's view
+  // (can be NULL). This happens delayed to avoid locking the UI.
+  void CreateRenderViewSoon(RenderWidgetHostView* host_view);
 
   // Sets |url_| and navigates |render_view_host_|.
   void NavigateToURL(const GURL& url);
@@ -138,10 +140,15 @@ class ExtensionHost : public RenderViewHostDelegate,
                        const NotificationDetails& details);
 
  private:
+  friend class ProcessCreationQueue;
+
   // Whether to allow DOM automation for created RenderViewHosts. This is used
   // for testing.
   static bool enable_dom_automation_;
 
+  // Actually create the RenderView for this host. See CreateRenderViewSoon.
+  void CreateRenderViewNow();
+
   // ExtensionFunctionDispatcher::Delegate
   // If this ExtensionHost has a view, this returns the Browser that view is a
   // part of.  If this is a global background page, we use the active Browser