Preparation to convert GetPrimaryAccount to return CoreAccountInfo

Change client code to work as if IdentityManager::GetPrimaryAccount
where returning a CoreAccountInfo instead of an AccountInfo. Method
will be updated in a followup CL.

This CL was uploaded by git cl split.

Bug: 926204
Change-Id: I963b34fe4bf1dac600e7859608c8090bbb05396b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1499539Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Auto-Submit: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637646}

chrome/browser/supervised_user/child_accounts/child_account_service.cc

@@ -101,8 +101,12 @@ void ChildAccountService::Init() {
 
   // If we're already signed in, check the account immediately just to be sure.
   // (We might have missed an update before registering as an observer.)
-  if (identity_manager_->HasPrimaryAccount())
-    OnExtendedAccountInfoUpdated(identity_manager_->GetPrimaryAccountInfo());
+  base::Optional<AccountInfo> primary_account_info =
+      identity_manager_->FindExtendedAccountInfoForAccount(
+          identity_manager_->GetPrimaryAccountInfo());
+
+  if (primary_account_info.has_value())
+    OnExtendedAccountInfoUpdated(primary_account_info.value());
 }
 
 bool ChildAccountService::IsChildAccountStatusKnown() {