Use thread-safe interface pointer in MdnsResponderAdapter.

The Mojo InterfacePtr is not thread-safe. The MdnsResponderAdapter,
which is the client of the mDNS responder service via a Mojo binding, is
created on the main thread to access the connector to the service
manager, while being used exclusively on a WebRTC work thread. As a
result, it should own a thread-safe InterfacePtr to the mDNS service.

Bug: 905566
Change-Id: I8395f4163d0d9f17b954d082a580af673bb107f3
Reviewed-on: https://chromium-review.googlesource.com/c/1351596Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Commit-Queue: Qingsi Wang <qingsi@google.com>
Cr-Commit-Position: refs/heads/master@{#611300}

content/renderer/p2p/mdns_responder_adapter.cc

@@ -39,22 +39,26 @@ void OnNameRemovedForAddress(
 }  // namespace
 
 MdnsResponderAdapter::MdnsResponderAdapter() {
+  network::mojom::MdnsResponderPtr client;
+  auto request = mojo::MakeRequest(&client);
+  thread_safe_client_ =
+      network::mojom::ThreadSafeMdnsResponderPtr::Create(std::move(client));
   ChildThreadImpl::current()->GetConnector()->BindInterface(
-      mojom::kBrowserServiceName, mojo::MakeRequest(&client_));
+      mojom::kBrowserServiceName, std::move(request));
 }
 
 MdnsResponderAdapter::~MdnsResponderAdapter() = default;
 
 void MdnsResponderAdapter::CreateNameForAddress(const rtc::IPAddress& addr,
                                                 NameCreatedCallback callback) {
-  client_->CreateNameForAddress(
+  thread_safe_client_->get()->CreateNameForAddress(
       jingle_glue::RtcIPAddressToNetIPAddress(addr),
       base::BindOnce(&OnNameCreatedForAddress, callback, addr));
 }
 
 void MdnsResponderAdapter::RemoveNameForAddress(const rtc::IPAddress& addr,
                                                 NameRemovedCallback callback) {
-  client_->RemoveNameForAddress(
+  thread_safe_client_->get()->RemoveNameForAddress(
       jingle_glue::RtcIPAddressToNetIPAddress(addr),
       base::BindOnce(&OnNameRemovedForAddress, callback));
 }

content/renderer/p2p/mdns_responder_adapter.h

@@ -32,7 +32,7 @@ class MdnsResponderAdapter : public webrtc::MdnsResponderInterface {
                             NameRemovedCallback callback) override;
 
  private:
-  network::mojom::MdnsResponderPtr client_;
+  scoped_refptr<network::mojom::ThreadSafeMdnsResponderPtr> thread_safe_client_;
 
   DISALLOW_COPY_AND_ASSIGN(MdnsResponderAdapter);
 };