arc: Add InstanceHelper::GetInstanceForMethod()

components/arc/net/arc_net_host_impl.cc

Index: components/arc/net/arc_net_host_impl.cc
diff --git a/components/arc/net/arc_net_host_impl.cc b/components/arc/net/arc_net_host_impl.cc
index 09caeb9c66c59b912175ddb08bfb8731a2972c43..22ca5abae2b5551caa8ea502e3820642f6d3d068 100644
--- a/components/arc/net/arc_net_host_impl.cc
+++ b/components/arc/net/arc_net_host_impl.cc
@@ -27,7 +27,10 @@
 
 namespace {
 
-const int kGetNetworksListLimit = 100;
+constexpr int kGetNetworksListLimit = 100;
+constexpr uint32_t kDefaultMinInstanceVersion = 0;
+constexpr uint32_t kDefaultNetworkChangedMinInstanceVersion = 2;
+constexpr uint32_t kWifiEnabledStateChanged = 3;
 
 chromeos::NetworkStateHandler* GetStateHandler() {
   return chromeos::NetworkHandler::Get()->network_state_handler();
@@ -572,16 +575,12 @@ void ArcNetHostImpl::StartScan() {
 }
 
 void ArcNetHostImpl::ScanCompleted(const chromeos::DeviceState* /*unused*/) {
-  if (!arc_bridge_service()->net()->instance()) {
-    VLOG(2) << "NetInstance not ready yet";
+  auto* net_instance = arc_bridge_service()->net()->GetInstanceForVersion(
+      kDefaultMinInstanceVersion, "ScanCompleted");

[Yusuke Sato, 2016/09/17 01:38:57]

nit: ScanCompleted has [MinVersion=1] but version 0 is queries here.

[Luis Héctor Chávez, 2016/09/17 01:56:11]

Done.

+  if (!net_instance)
     return;
-  }
-  if (arc_bridge_service()->net()->version() < 1) {
-    VLOG(1) << "NetInstance does not support ScanCompleted.";
-    return;
-  }
 
-  arc_bridge_service()->net()->instance()->ScanCompleted();
+  net_instance->ScanCompleted();
 }
 
 void ArcNetHostImpl::GetDefaultNetwork(
@@ -605,29 +604,28 @@ void ArcNetHostImpl::GetDefaultNetwork(
 void ArcNetHostImpl::DefaultNetworkSuccessCallback(
     const std::string& service_path,
     const base::DictionaryValue& dictionary) {
-  if (!arc_bridge_service()->net()->instance()) {
-    VLOG(2) << "NetInstance is null.";
+  auto* net_instance = arc_bridge_service()->net()->GetInstanceForVersion(
+      kDefaultMinInstanceVersion, "DefaultNetworkChanged");

[Yusuke Sato, 2016/09/17 01:38:57]

Ok, then could you document why kDefaultMinInstanceVersion is used here?

[Luis Héctor Chávez, 2016/09/17 01:56:11]

Oh there was a bug here! This should have been
kDefaultNetworkChangedMinInstanceVersion.

+  if (!net_instance)
     return;
-  }
-  arc_bridge_service()->net()->instance()->DefaultNetworkChanged(
-      TranslateONCConfiguration(&dictionary),
-      TranslateONCConfiguration(&dictionary));
+
+  net_instance->DefaultNetworkChanged(TranslateONCConfiguration(&dictionary),
+                                      TranslateONCConfiguration(&dictionary));
 }
 
 void ArcNetHostImpl::DefaultNetworkChanged(
     const chromeos::NetworkState* network) {
-  if (arc_bridge_service()->net()->version() < 2) {
-    VLOG(1) << "ArcBridgeService does not support DefaultNetworkChanged.";
-    return;
-  }
-
   if (!network) {
     VLOG(1) << "No default network";
-    arc_bridge_service()->net()->instance()->DefaultNetworkChanged(nullptr,
-                                                                   nullptr);
+    net_instance->DefaultNetworkChanged(nullptr, nullptr);

[Yusuke Sato, 2016/09/17 01:38:57]

nit: this won't compile :)

I meant something like:

 if (!network) {
   VLOG(1) << "No ...";
   auto* net_instance = ...;
   if (net_instance)
     net_instance->DefaultNetworkChanged(...);
   return;
 }

[Luis Héctor Chávez, 2016/09/17 01:56:11]

Yeah, realized this too late :P Done.

     return;
   }
 
+  auto* net_instance = arc_bridge_service()->net()->GetInstanceForVersion(
+      kDefaultNetworkChangedMinInstanceVersion, "DefaultNetworkChanged");

[Yusuke Sato, 2016/09/17 01:38:57]

..and then, why this one was okay to use
kDefaultNetworkChangedMinInstanceVersion?

[Luis Héctor Chávez, 2016/09/17 01:56:11]

Both should use it.

+  if (!net_instance)
+    return;
+
   VLOG(1) << "New default network: " << network->path();
   std::string user_id_hash = chromeos::LoginState::Get()->primary_user_hash();
   GetManagedConfigurationHandler()->GetProperties(
@@ -638,14 +636,14 @@ void ArcNetHostImpl::DefaultNetworkChanged(
 }
 
 void ArcNetHostImpl::DeviceListChanged() {
-  if (arc_bridge_service()->net()->version() < 3) {
-    VLOG(1) << "ArcBridgeService does not support DeviceListChanged.";
+  auto* net_instance = arc_bridge_service()->net()->GetInstanceForVersion(
+      kWifiEnabledStateChanged, "WifiEnabledStateChanged");
+  if (!net_instance)
     return;
-  }
 
   bool is_enabled = GetStateHandler()->IsTechnologyEnabled(
       chromeos::NetworkTypePattern::WiFi());
-  arc_bridge_service()->net()->instance()->WifiEnabledStateChanged(is_enabled);
+  net_instance->WifiEnabledStateChanged(is_enabled);
 }
 
 void ArcNetHostImpl::OnShuttingDown() {