arc: Reduce logspam when ARC is not enabled/available

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 be17b60cc45eb144608db2a4e0ee234b53d6640a..938a824ddd54e2dee3118af9fc48a77be7451d1b 100644
--- a/components/arc/net/arc_net_host_impl.cc
+++ b/components/arc/net/arc_net_host_impl.cc
@@ -293,13 +293,12 @@ namespace arc {
 ArcNetHostImpl::ArcNetHostImpl(ArcBridgeService* bridge_service)
     : ArcService(bridge_service), binding_(this), weak_factory_(this) {
   arc_bridge_service()->net()->AddObserver(this);
-  GetStateHandler()->AddObserver(this, FROM_HERE);
 }
 
 ArcNetHostImpl::~ArcNetHostImpl() {
   DCHECK(thread_checker_.CalledOnValidThread());
   arc_bridge_service()->net()->RemoveObserver(this);
-  if (chromeos::NetworkHandler::IsInitialized()) {
+  if (observing_network_state_) {

[Yusuke Sato, 2016/11/30 23:29:39]

Do we need the check? I think the convention in Chromium is that
RemoveObserver(p) is no-op when |p| is not in the list.

[Luis Héctor Chávez, 2016/11/30 23:45:08]

Yes, but
https://cs.chromium.org/chromium/src/chromeos/network/network_state_handler.c...
also does logging. It might be a bit confusing for the log readers to see that
something is unregistering but never registering for event notification.

[Yusuke Sato, 2016/11/30 23:59:30]

Acknowledged.

     GetStateHandler()->RemoveObserver(this, FROM_HERE);
   }
 }
@@ -312,6 +311,19 @@ void ArcNetHostImpl::OnInstanceReady() {
   auto* instance = arc_bridge_service()->net()->GetInstanceForMethod("Init");
   DCHECK(instance);
   instance->Init(std::move(host));
+
+  if (chromeos::NetworkHandler::IsInitialized()) {
+    GetStateHandler()->AddObserver(this, FROM_HERE);
+    observing_network_state_ = true;
+  }
+}
+
+void ArcNetHostImpl::OnInstanceClosed() {
+  if (!observing_network_state_)

[Yusuke Sato, 2016/11/30 23:29:39]

same

+    return;
+
+  GetStateHandler()->RemoveObserver(this, FROM_HERE);
+  observing_network_state_ = false;
 }
 
 void ArcNetHostImpl::GetNetworksDeprecated(
@@ -647,7 +659,9 @@ void ArcNetHostImpl::DeviceListChanged() {
 }
 
 void ArcNetHostImpl::OnShuttingDown() {
+  DCHECK(observing_network_state_);

[Yusuke Sato, 2016/11/30 23:29:39]

same

   GetStateHandler()->RemoveObserver(this, FROM_HERE);
+  observing_network_state_ = false;
 }
 
 }  // namespace arc