Adds DNS prefetch support to Chromecast.

chromecast/browser/url_request_context_factory.h

Index: chromecast/browser/url_request_context_factory.h
diff --git a/chromecast/browser/url_request_context_factory.h b/chromecast/browser/url_request_context_factory.h
index 0b9a4e955e012bc74a619bcba613121317f1a54b..5ae43cb7a4a626853a7c3a6d28ee140f30038b89 100644
--- a/chromecast/browser/url_request_context_factory.h
+++ b/chromecast/browser/url_request_context_factory.h
@@ -48,6 +48,10 @@ class URLRequestContextFactory {
     return app_network_delegate_.get();
   }
 
+  net::HostResolver* host_resolver() const {
+    return host_resolver_.get();
+  }
+
   // Initialize the CastNetworkDelegate objects. This needs to be done
   // after the CastService is created, but before any URL requests are made.
   void InitializeNetworkDelegates();