Make BackgroundContentsService start up BackgroundContents with a delay, as for ExtensionHosts.

extensions/browser/extension_host_delegate.h

Index: extensions/browser/extension_host_delegate.h
diff --git a/extensions/browser/extension_host_delegate.h b/extensions/browser/extension_host_delegate.h
index 71c0990dc83e8847d5338f57d44f0d161826c098..86726ff0dc84e4f76b7f072a1bf4d8548d5aa18e 100644
--- a/extensions/browser/extension_host_delegate.h
+++ b/extensions/browser/extension_host_delegate.h
@@ -22,6 +22,7 @@ class Rect;
 namespace extensions {
 class Extension;
 class ExtensionHost;
+class ExtensionHostQueue;
 
 // A delegate to support functionality that cannot exist in the extensions
 // module. This is not an inner class of ExtensionHost to allow it to be forward
@@ -64,6 +65,10 @@ class ExtensionHostDelegate {
                                           const GURL& security_origin,
                                           content::MediaStreamType type,
                                           const Extension* extension) = 0;
+
+  // Returns the ExtensionHostQueue implementation to use for creating
+  // ExtensionHost renderers.
+  virtual ExtensionHostQueue* GetExtensionHostQueue() const = 0;
 };
 
 }  // namespace extensions