Handle correctly the situation when PasswordStore is destroyed on the UI thread.

PasswordStore uses SKIP_ON_SHUTDOWN for background sequence. That means that PasswordStore::DestroyOnBackgroundThread() can be skipped. In this case PasswordStore::* may be destroyed on the UI thread.
It's not a problem for PasswordSyncableService. We just need to remove the check in the destructor.
PasswordReuseDetector has this check implicitly via base::CancelableTaskTracker. Thus, we can just leak the object.

Bug: 741660
Change-Id: Ic49cb068733c159bca55e8d76eb58f70793f5fbe
Reviewed-on: https://chromium-review.googlesource.com/598008Reviewed-by: Vadym Doroshenko <dvadym@chromium.org>
Commit-Queue: Vasilii Sukhanov <vasilii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491422}

components/password_manager/core/browser/password_store.cc

@@ -778,9 +778,9 @@ void PasswordStore::InitOnBackgroundThread(
   syncable_service_->InjectStartSyncFlare(flare);
 // TODO(crbug.com/706392): Fix password reuse detection for Android.
 #if !defined(OS_ANDROID) && !defined(OS_IOS)
-  reuse_detector_ = base::MakeUnique<PasswordReuseDetector>();
+  reuse_detector_ = new PasswordReuseDetector;
   GetAutofillableLoginsImpl(
-      base::MakeUnique<GetLoginsRequest>(reuse_detector_.get()));
+      base::MakeUnique<GetLoginsRequest>(reuse_detector_));
 #endif
 }
 
@@ -789,7 +789,8 @@ void PasswordStore::DestroyOnBackgroundThread() {
   syncable_service_.reset();
 // TODO(crbug.com/706392): Fix password reuse detection for Android.
 #if !defined(OS_ANDROID) && !defined(OS_IOS)
-  reuse_detector_.reset();
+  delete reuse_detector_;
+  reuse_detector_ = nullptr;
 #endif
 }
 

components/password_manager/core/browser/password_store.h

@@ -16,6 +16,7 @@
 #include "base/observer_list_threadsafe.h"
 #include "base/sequenced_task_runner.h"
 #include "base/time/time.h"
+#include "build/build_config.h"
 #include "components/keyed_service/core/refcounted_keyed_service.h"
 #include "components/password_manager/core/browser/password_reuse_defines.h"
 #include "components/password_manager/core/browser/password_store_change.h"
@@ -583,7 +584,8 @@ class PasswordStore : protected PasswordStoreSync,
   void InitOnBackgroundThread(
       const syncer::SyncableService::StartSyncFlare& flare);
 
-  // Deletes objest that should be destroyed on the background thread.
+  // Deletes object that should be destroyed on the background thread.
+  // WARNING: this method can be skipped on shutdown.
   void DestroyOnBackgroundThread();
 
   // The observers.
@@ -593,7 +595,10 @@ class PasswordStore : protected PasswordStoreSync,
   std::unique_ptr<AffiliatedMatchHelper> affiliated_match_helper_;
 // TODO(crbug.com/706392): Fix password reuse detection for Android.
 #if !defined(OS_ANDROID) && !defined(OS_IOS)
-  std::unique_ptr<PasswordReuseDetector> reuse_detector_;
+  // PasswordReuseDetector can be only destroyed on the background thread. It
+  // can't be owned by PasswordStore because PasswordStore can be destroyed on
+  // UI thread and DestroyOnBackgroundThread isn't guaranteed to be called.
+  PasswordReuseDetector* reuse_detector_ = nullptr;
 #endif
 #if defined(SYNC_PASSWORD_REUSE_DETECTION_ENABLED)
   std::unique_ptr<PasswordStoreSigninNotifier> notifier_;

components/password_manager/core/browser/password_syncable_service.cc

@@ -340,9 +340,7 @@ PasswordSyncableService::PasswordSyncableService(
       clock_(new base::DefaultClock),
       is_processing_sync_changes_(false) {}
 
-PasswordSyncableService::~PasswordSyncableService() {
-  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
-}
+PasswordSyncableService::~PasswordSyncableService() = default;
 
 syncer::SyncMergeResult PasswordSyncableService::MergeDataAndStartSyncing(
     syncer::ModelType type,