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

extensions/browser/extension_host_queue.h

Index: extensions/browser/extension_host_queue.h
diff --git a/extensions/browser/extension_host_queue.h b/extensions/browser/extension_host_queue.h
index 4c9cb5bfa000432ea7adaee1e21402b2f9e33e5b..387a2b6d67e16ef513315ddd2d63c6c50bce2515 100644
--- a/extensions/browser/extension_host_queue.h
+++ b/extensions/browser/extension_host_queue.h
@@ -7,7 +7,7 @@
 
 namespace extensions {
 
-class ExtensionHost;
+class DelayedStartRenderHost;
 
 // An interface for a queue of ExtensionHosts waiting for initialization.
 // This is used to implement different throttling strategies.
@@ -16,11 +16,11 @@ class ExtensionHostQueue {
   virtual ~ExtensionHostQueue() {}
 
   // Adds a host to the queue for RenderView creation.
-  virtual void Add(ExtensionHost* host) = 0;
+  virtual void Add(DelayedStartRenderHost* host) = 0;
 
   // Removes a host from the queue (for example, it may be deleted before
   // having a chance to start).
-  virtual void Remove(ExtensionHost* host) = 0;
+  virtual void Remove(DelayedStartRenderHost* host) = 0;
 };
 
 }  // namespace extensions