Add a helper method to retrieve network service from a service manager Connector

If services are launched without full browser process, they need to retrieve
the network service from the service manager connector they have.
This CL adds a helper method to allow that to work.

BUG=695115

Change-Id: I362b814b03d60d9645523664a7243555bac6f053
Reviewed-on: https://chromium-review.googlesource.com/1188776Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586094}

content/browser/network_service_instance.cc

@@ -46,16 +46,24 @@ void BindNetworkChangeManagerRequest(
 }  // namespace
 
 network::mojom::NetworkService* GetNetworkService() {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  service_manager::Connector* connector =
+      base::FeatureList::IsEnabled(network::features::kNetworkService)
+          ? ServiceManagerConnection::GetForProcess()->GetConnector()
+          : nullptr;
+  return GetNetworkServiceFromConnector(connector);
+}
 
+CONTENT_EXPORT network::mojom::NetworkService* GetNetworkServiceFromConnector(
+    service_manager::Connector* connector) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   if (!g_network_service_ptr)
     g_network_service_ptr = new network::mojom::NetworkServicePtr;
   static NetworkServiceClient* g_client;
   if (!g_network_service_ptr->is_bound() ||
       g_network_service_ptr->encountered_error()) {
     if (base::FeatureList::IsEnabled(network::features::kNetworkService)) {
-      ServiceManagerConnection::GetForProcess()->GetConnector()->BindInterface(
-          mojom::kNetworkServiceName, g_network_service_ptr);
+      connector->BindInterface(mojom::kNetworkServiceName,
+                               g_network_service_ptr);
     } else {
       DCHECK(!g_network_service_ptr->is_bound());
       BrowserThread::PostTask(

content/public/browser/network_service_instance.h

@@ -15,6 +15,10 @@ class NetworkService;
 }
 }  // namespace network
 
+namespace service_manager {
+class Connector;
+}  // namespace service_manager
+
 namespace content {
 
 // Returns a pointer to the NetworkService, creating / re-creating it as needed.
@@ -25,6 +29,14 @@ namespace content {
 // This method can only be called on the UI thread.
 CONTENT_EXPORT network::mojom::NetworkService* GetNetworkService();
 
+// Similar to GetNetworkService(), but will create the NetworkService from a
+// service manager connector if needed. If network service is disabled,
+// |connector| will be ignored and this method is identical to
+// GetNetworkService().
+// This method can only be called on the UI thread.
+CONTENT_EXPORT network::mojom::NetworkService* GetNetworkServiceFromConnector(
+    service_manager::Connector* connector);
+
 // When network service is disabled, returns the in-process NetworkService
 // pointer which is used to ease transition to network service.
 // Must only be called on the IO thread.  Must not be called if the network