First pass at fixing guest browser cookies issue.

chrome/browser/history/in_memory_url_index.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/history/in_memory_url_index.h"
 
 #include "base/files/file_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/trace_event/trace_event.h"
 #include "chrome/browser/history/history_service.h"
@@ skipping 104 matching lines @@
   if (history_service_) {
     history_service_->RemoveObserver(this);
     history_service_ = nullptr;
   }
   cache_reader_tracker_.TryCancelAll();
   shutdown_ = true;
   base::FilePath path;
   if (!GetCacheFilePath(&path))
     return;
   private_data_tracker_.TryCancelAll();
-  URLIndexPrivateData::WritePrivateDataToCacheFileTask(private_data_, path);
+
+  // During browser TearDown this method was called from a thread that can
+  // perform FILE ops. Guest Profiles are closed on UI thread, so post a task.
+  if (content::BrowserThread::CurrentlyOn(content::BrowserThread::FILE))
+    URLIndexPrivateData::WritePrivateDataToCacheFileTask(private_data_, path);
+  else
+    PostSaveToCacheFileTask();
   needs_to_be_cached_ = false;
 }
 
 void InMemoryURLIndex::ClearPrivateData() {
   private_data_->Clear();
 }
 
 bool InMemoryURLIndex::GetCacheFilePath(base::FilePath* file_path) {
   if (history_dir_.empty())
     return false;
@@ skipping 188 matching lines @@
         base::Bind(DeleteCacheFile, path));
   }
 }
 
 void InMemoryURLIndex::OnCacheSaveDone(bool succeeded) {
   if (save_cache_observer_)
     save_cache_observer_->OnCacheSaveFinished(succeeded);
 }
 
 }  // namespace history