Implement ServiceWorkerFetchDispatcher::MaybeStartNavigationPreload().

content/browser/loader/resource_dispatcher_host_impl.h

Index: content/browser/loader/resource_dispatcher_host_impl.h
diff --git a/content/browser/loader/resource_dispatcher_host_impl.h b/content/browser/loader/resource_dispatcher_host_impl.h
index 006c5eed43ecf73138ebfab0b6ebe1c6b2ff8739..80c648dcb814a3df0ae8e8a1bb161aee79526dca 100644
--- a/content/browser/loader/resource_dispatcher_host_impl.h
+++ b/content/browser/loader/resource_dispatcher_host_impl.h
@@ -337,6 +337,10 @@ class CONTENT_EXPORT ResourceDispatcherHostImpl
 
   bool is_shutdown() const { return is_shutdown_; }
 
+  // Creates a new request ID for browser initiated requests. See the comments
+  // of |request_id_| for the details.
+  int MakeRequestID() { return --request_id_; }

[mmenke, 2016/10/19 14:56:02]

Could you make this DCHECK that we're on the IO thread, and move it to the cc
file?

[horo, 2016/10/19 15:18:53]

Done.

+
  private:
   friend class ResourceDispatcherHostTest;