Open the LoginDatabase on the DB thread, not the UI thread.

chrome/browser/password_manager/password_store_mac.h

Index: chrome/browser/password_manager/password_store_mac.h
diff --git a/chrome/browser/password_manager/password_store_mac.h b/chrome/browser/password_manager/password_store_mac.h
index ecde48523792c78583a41f5921356ad170765ceb..7d3194e89709018314e9398f5731b95dc1190690 100644
--- a/chrome/browser/password_manager/password_store_mac.h
+++ b/chrome/browser/password_manager/password_store_mac.h
@@ -8,6 +8,7 @@
 #include <vector>
 
 #include "base/callback_forward.h"
+#include "base/files/file_path.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/threading/thread.h"
 #include "components/password_manager/core/browser/login_database.h"
@@ -34,7 +35,7 @@ class PasswordStoreMac : public password_manager::PasswordStore {
       scoped_refptr<base::SingleThreadTaskRunner> main_thread_runner,
       scoped_refptr<base::SingleThreadTaskRunner> db_thread_runner,
       crypto::AppleKeychain* keychain,
-      password_manager::LoginDatabase* login_db);
+      const base::FilePath& login_db_file_path);
 
   // Initializes |thread_|.
   bool Init(const syncer::SyncableService::StartSyncFlare& flare) override;
@@ -42,9 +43,17 @@ class PasswordStoreMac : public password_manager::PasswordStore {
   // Stops |thread_|.
   void Shutdown() override;
 
+  // Used for testing.
+  password_manager::LoginDatabase* login_metadata_db() const {
+    return login_metadata_db_.get();
+  }
+
  protected:
   ~PasswordStoreMac() override;
 
+  // Opens |login_metadata_db_| on the background thread.
+  void InitOnBackgroundThread();
+
   scoped_refptr<base::SingleThreadTaskRunner> GetBackgroundTaskRunner()
       override;
 
@@ -97,6 +106,7 @@ class PasswordStoreMac : public password_manager::PasswordStore {
   void CleanOrphanedForms(std::vector<autofill::PasswordForm*>* forms);
 
   scoped_ptr<crypto::AppleKeychain> keychain_;
+  base::FilePath login_db_file_path_;
   scoped_ptr<password_manager::LoginDatabase> login_metadata_db_;
 
   // Thread that the synchronous methods are run on.