Stop deleting ShortcutsDatabase on the UI thread during shutdown

chrome/browser/autocomplete/shortcuts_backend.cc

Index: chrome/browser/autocomplete/shortcuts_backend.cc
diff --git a/chrome/browser/autocomplete/shortcuts_backend.cc b/chrome/browser/autocomplete/shortcuts_backend.cc
index 4da4f902022bc6628f85e69fe59a42c82048d8ce..003be7055b202d7f3f00ae55f62010fb16cee093 100644
--- a/chrome/browser/autocomplete/shortcuts_backend.cc
+++ b/chrome/browser/autocomplete/shortcuts_backend.cc
@@ -146,6 +146,13 @@ void ShortcutsBackend::AddOrUpdateShortcut(const base::string16& text,
 }
 
 ShortcutsBackend::~ShortcutsBackend() {
+  if (db_) {
+    auto* db = db_.get();
+    db->AddRef();
+    db_ = nullptr;
+    if (!BrowserThread::ReleaseSoon(BrowserThread::DB, FROM_HERE, db))
+      db->Release();
+  }
 }
 
 // static