Move observing logic to Init/Shutdown in ChildAccountService

ChildAccountService listens to GaiaCookieManagerService for
notifications about signed in/out accounts. The code was starting to
observe in the constructor and stopping in the destructor. That is not
totally correct as services should start observing in Init() and stop
on Shutdown(). Moved the AddObserver/RemoveObserver calls to their
proper locations.

Bug: 921007
Change-Id: I6a0afef6845ab59c2f7bf4994cb8a9c90b8ef034
Reviewed-on: https://chromium-review.googlesource.com/c/1454500Reviewed-by: Marc Treib <treib@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Sergio Villar <svillar@igalia.com>
Cr-Commit-Position: refs/heads/master@{#629596}

chrome/browser/supervised_user/child_accounts/child_account_service.cc

@@ -77,11 +77,9 @@ ChildAccountService::ChildAccountService(Profile* profile)
       gaia_cookie_manager_(
           GaiaCookieManagerServiceFactory::GetForProfile(profile)),
       weak_ptr_factory_(this) {
-  gaia_cookie_manager_->AddObserver(this);
 }
 
 ChildAccountService::~ChildAccountService() {
-  gaia_cookie_manager_->RemoveObserver(this);
 }
 
 // static
@@ -102,6 +100,7 @@ void ChildAccountService::RegisterProfilePrefs(
 
 void ChildAccountService::Init() {
   SupervisedUserServiceFactory::GetForProfile(profile_)->SetDelegate(this);
+  gaia_cookie_manager_->AddObserver(this);
   IdentityManagerFactory::GetForProfile(profile_)->AddObserver(this);
 
   PropagateChildStatusToUser(profile_->IsChild());
@@ -121,6 +120,7 @@ bool ChildAccountService::IsChildAccountStatusKnown() {
 void ChildAccountService::Shutdown() {
   family_fetcher_.reset();
   IdentityManagerFactory::GetForProfile(profile_)->RemoveObserver(this);
+  gaia_cookie_manager_->RemoveObserver(this);
   SupervisedUserServiceFactory::GetForProfile(profile_)->SetDelegate(nullptr);
   DCHECK(!active_);
 }