Stop deleting ShortcutsDatabase on the UI thread during shutdown

chrome/browser/autocomplete/shortcuts_backend.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/autocomplete/shortcuts_backend.h"
 
 #include <map>
 #include <string>
 #include <vector>
 
@@ skipping 128 matching lines @@
           it->second.id, text, MatchToMatchCore(match, profile_), now,
           it->second.number_of_hits + 1));
       return;
     }
   }
   AddShortcut(ShortcutsDatabase::Shortcut(
       base::GenerateGUID(), text, MatchToMatchCore(match, profile_), now, 1));
 }
 
 ShortcutsBackend::~ShortcutsBackend() {
+  if (db_) {
+    auto* db = db_.get();
+    db->AddRef();
+    db_ = nullptr;
+    if (!BrowserThread::ReleaseSoon(BrowserThread::DB, FROM_HERE, db))
+      db->Release();
+  }
 }
 
 // static
 ShortcutsDatabase::Shortcut::MatchCore ShortcutsBackend::MatchToMatchCore(
     const AutocompleteMatch& match,
     Profile* profile) {
   const AutocompleteMatch::Type match_type = GetTypeForShortcut(match.type);
   TemplateURLService* service =
       TemplateURLServiceFactory::GetForProfile(profile);
   const AutocompleteMatch& normalized_match =
@@ skipping 177 matching lines @@
   guid_map_.clear();
   FOR_EACH_OBSERVER(ShortcutsBackendObserver, observer_list_,
                     OnShortcutsChanged());
   return no_db_access_ ||
          BrowserThread::PostTask(
              BrowserThread::DB, FROM_HERE,
              base::Bind(
                  base::IgnoreResult(&ShortcutsDatabase::DeleteAllShortcuts),
                  db_.get()));
 }