ProfileSyncService: Handle null SupervisedUserService

chrome/browser/sync/chrome_sync_client.cc

Index: chrome/browser/sync/chrome_sync_client.cc
diff --git a/chrome/browser/sync/chrome_sync_client.cc b/chrome/browser/sync/chrome_sync_client.cc
index 6a489904cb124e421cfa86dd44245c65dfc1c0d5..4151c8ae089dfb9abbb1c6db9c0a2e98b0a6ab2d 100644
--- a/chrome/browser/sync/chrome_sync_client.cc
+++ b/chrome/browser/sync/chrome_sync_client.cc
@@ -447,10 +447,15 @@ ChromeSyncClient::GetSyncableServiceForType(syncer::ModelType type) {
       return SupervisedUserSharedSettingsServiceFactory::GetForBrowserContext(
           profile_)->AsWeakPtr();
 #endif  // !defined(OS_ANDROID)
-    case syncer::SUPERVISED_USER_WHITELISTS:
-      return SupervisedUserServiceFactory::GetForProfile(profile_)
-          ->GetWhitelistService()
-          ->AsWeakPtr();
+    case syncer::SUPERVISED_USER_WHITELISTS: {
+      // SupervisedUserServiceFactory depends on ProfileSyncServiceFactory

[skym, 2017/05/01 17:24:03]

I'd rephrase this to talk about the dep in the other direction.

// Unlike other types here, ProfileSyncServiceFactory does not declare a
DependsOn the SupervisedUserServiceFactory (in order to avoid circular
dependency), which means we cannot assume it is still alive.

[Marc Treib, 2017/05/02 08:27:36]

+1

[rishiag, 2017/05/05 17:22:02]

Done.

+      // so SupervisedUserService might be destroyed before ProfileSyncService.
+      SupervisedUserService* supervised_user_service =
+          SupervisedUserServiceFactory::GetForProfile(profile_);

[Marc Treib, 2017/05/02 08:27:36]

SupervisedUserServiceFactory::GetForProfile will create the service if it
doesn't exist. I don't know what will happen if this gets called after the SUS
has already been destroyed, but I assume nothing good?
We should probably add a GetForProfileIfExists method on the SUSFactory.

[rishiag, 2017/05/05 17:22:02]

Done.

+      if (supervised_user_service)
+        return supervised_user_service->GetWhitelistService()->AsWeakPtr();
+      return base::WeakPtr<syncer::SyncableService>();
+    }
 #endif  // BUILDFLAG(ENABLE_SUPERVISED_USERS)
     case syncer::ARTICLES: {
       dom_distiller::DomDistillerService* service =
@@ -507,7 +512,7 @@ ChromeSyncClient::GetSyncBridgeForModelType(syncer::ModelType type) {
           ->AsWeakPtr();
 #endif  // defined(OS_CHROMEOS)
     case syncer::TYPED_URLS:
-      // TODO(gangwu):implement TypedURLSyncBridge and return real
+      // TODO(gangwu): Implement TypedURLSyncBridge and return real
       // TypedURLSyncBridge here.
       return base::WeakPtr<syncer::ModelTypeSyncBridge>();
     default: