arc: Fix issue when Arc OptIn is not started on fresh devices.

chrome/browser/chromeos/arc/arc_auth_service.cc

Index: chrome/browser/chromeos/arc/arc_auth_service.cc
diff --git a/chrome/browser/chromeos/arc/arc_auth_service.cc b/chrome/browser/chromeos/arc/arc_auth_service.cc
index 0781a0124631387d85c13cfb7c5d9cf4099043be..fc2082532984647f5fba446fcc7aff130bf89d45 100644
--- a/chrome/browser/chromeos/arc/arc_auth_service.cc
+++ b/chrome/browser/chromeos/arc/arc_auth_service.cc
@@ -228,10 +228,8 @@ void ArcAuthService::OnPrimaryUserProfilePrepared(Profile* profile) {
       OnOptInPreferenceChanged();
     } else {
       UpdateEnabledStateUMA(false);
-      if (!disable_ui_for_testing && profile_->IsNewProfile()) {
-        PrefServiceSyncableFromProfile(profile_)->AddObserver(this);
-        OnIsSyncingChanged();
-      }
+      PrefServiceSyncableFromProfile(profile_)->AddObserver(this);

[khmel, 2016/03/31 22:19:21]

In one of the recent CLs I changed observer scheme 

from:
PrefChangeRegistrar pref_change_registrar_;
pref_change_registrar_.Add(prefs::kArcEnabled, ...)

To:
PrefServiceSyncableFromProfile(profile_)->
AddSyncedPrefObserver(prefs::kArcEnabled, this);

This was done to handle UMA statics properly in order to filter local vs synced
changes.

However SyncedPrefObserver is not triggered when initial sync occurred (for new
profile).
Workaround is to double check ArcEnabled pref on syncing is ready.

I also tested following case:
Enabled Arc on device, Logout, Disable Arc on another device,
Restart device and change was tracked. In this case, it was synced.

WDYT?

+      OnIsSyncingChanged();
     }
   } else {
     auth_code_.clear();
@@ -246,8 +244,14 @@ void ArcAuthService::OnIsSyncingChanged() {
     return;
 
   pref_service_syncable->RemoveObserver(this);
-  if (!profile_->GetPrefs()->HasPrefPath(prefs::kArcEnabled))
+
+  if (profile_->GetPrefs()->GetBoolean(prefs::kArcEnabled))
+    OnOptInPreferenceChanged();
+
+  if (!disable_ui_for_testing && profile_->IsNewProfile() &&

[xiyuan, 2016/03/31 22:32:44]

nit: profile_->IsNewProfile() might not be necessary.

[khmel, 2016/03/31 22:47:34]

I think it might be required.
For example:
User starts first time and we show Notification. User ignores this and
notification is timed out. User starts next time, in this case profile is not
new, but it still has no kArcEnabled path. In this case we would show
notification second time and this is not expected from UI design.

[xiyuan, 2016/03/31 22:50:50]

Okay. That sounds like a valid case.

+      !profile_->GetPrefs()->HasPrefPath(prefs::kArcEnabled)) {
     arc::ArcAuthNotification::Show();
+  }
 }
 
 void ArcAuthService::Shutdown() {