Bind new mojom HostResolvers asynchronously.

Binding new HostResolvers asynchronously gives them slightly longer to
set up before they might be used by a consumer. Some host resolvers may
need to obtain the system config asynchronously during setup.

Bug: 1041045
Change-Id: Ia238e7eb77ac0551d4bfa282c2dcde14cc279fec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1995369
Commit-Queue: Katharine Daly <dalyk@google.com>
Reviewed-by: Eric Orth <ericorth@chromium.org>
Cr-Commit-Position: refs/heads/master@{#733061}

services/network/host_resolver.cc

@@ -54,12 +54,16 @@ HostResolver::HostResolver(
     ConnectionShutdownCallback connection_shutdown_callback,
     net::HostResolver* internal_resolver,
     net::NetLog* net_log)
-    : receiver_(this, std::move(resolver_receiver)),
+    : receiver_(this),
+      pending_receiver_(std::move(resolver_receiver)),
       connection_shutdown_callback_(std::move(connection_shutdown_callback)),
       internal_resolver_(internal_resolver),
       net_log_(net_log) {
-  receiver_.set_disconnect_handler(
-      base::BindOnce(&HostResolver::OnConnectionError, base::Unretained(this)));
+  // Bind the pending receiver asynchronously to give the resolver a chance
+  // to set up (some resolvers need to obtain the system config asynchronously).
+  base::SequencedTaskRunnerHandle::Get()->PostTask(
+      FROM_HERE,
+      base::BindOnce(&HostResolver::AsyncSetUp, weak_factory_.GetWeakPtr()));
 }
 
 HostResolver::HostResolver(net::HostResolver* internal_resolver,
@@ -140,6 +144,12 @@ void HostResolver::SetResolveHostCallbackForTesting(
   resolve_host_callback.Get() = std::move(callback);
 }
 
+void HostResolver::AsyncSetUp() {
+  receiver_.Bind(std::move(pending_receiver_));
+  receiver_.set_disconnect_handler(
+      base::BindOnce(&HostResolver::OnConnectionError, base::Unretained(this)));
+}
+
 void HostResolver::OnResolveHostComplete(ResolveHostRequest* request,
                                          int error) {
   DCHECK_NE(net::ERR_IO_PENDING, error);

services/network/host_resolver.h

@@ -13,6 +13,7 @@
 #include "base/component_export.h"
 #include "base/containers/unique_ptr_adapters.h"
 #include "base/macros.h"
+#include "base/memory/weak_ptr.h"
 #include "mojo/public/cpp/bindings/pending_receiver.h"
 #include "mojo/public/cpp/bindings/pending_remote.h"
 #include "mojo/public/cpp/bindings/receiver.h"
@@ -68,11 +69,13 @@ class COMPONENT_EXPORT(NETWORK_SERVICE) HostResolver
   static void SetResolveHostCallbackForTesting(ResolveHostCallback callback);
 
  private:
+  void AsyncSetUp();
   void OnResolveHostComplete(ResolveHostRequest* request, int error);
   void OnMdnsListenerCancelled(HostResolverMdnsListener* listener);
   void OnConnectionError();
 
   mojo::Receiver<mojom::HostResolver> receiver_;
+  mojo::PendingReceiver<mojom::HostResolver> pending_receiver_;
   ConnectionShutdownCallback connection_shutdown_callback_;
   std::set<std::unique_ptr<ResolveHostRequest>, base::UniquePtrComparator>
       requests_;
@@ -82,6 +85,8 @@ class COMPONENT_EXPORT(NETWORK_SERVICE) HostResolver
   net::HostResolver* const internal_resolver_;
   net::NetLog* const net_log_;
 
+  base::WeakPtrFactory<HostResolver> weak_factory_{this};
+
   DISALLOW_COPY_AND_ASSIGN(HostResolver);
 };