drive: Rewrite UpdateOpreation to access cache/metadata on the blocking pool

chrome/browser/chromeos/drive/file_cache_unittest.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/chromeos/drive/file_cache.h"
 
 #include <string>
 #include <vector>
 
 #include "base/file_util.h"
@@ skipping 318 matching lines @@
       const std::string& resource_id,
       const std::string& md5,
       FileError expected_error,
       int expected_cache_state,
       FileCache::CacheSubDirectoryType expected_sub_dir_type) {
     expected_error_ = expected_error;
     expected_cache_state_ = expected_cache_state;
     expected_sub_dir_type_ = expected_sub_dir_type;
 
     FileError error = FILE_ERROR_OK;
-    cache_->ClearDirtyOnUIThread(
-        resource_id, md5,
+    PostTaskAndReplyWithResult(
+        blocking_task_runner_,
+        FROM_HERE,
+        base::Bind(&FileCache::ClearDirty,
+                   base::Unretained(cache_.get()),
+                   resource_id, md5),
         google_apis::test_util::CreateCopyResultCallback(&error));
     google_apis::test_util::RunBlockingPoolTask();
     VerifyCacheFileState(error, resource_id, md5);
   }
 
   void TestMarkAsMounted(
       const std::string& resource_id,
       const std::string& md5,
       FileError expected_error,
       int expected_cache_state,
@@ skipping 961 matching lines @@
       google_apis::test_util::GetTestFilePath("chromeos/gdata/empty_feed.json"),
       FILE_ERROR_OK,
       test_util::TEST_CACHE_STATE_PRESENT |
       test_util::TEST_CACHE_STATE_PINNED |
       test_util::TEST_CACHE_STATE_PERSISTENT,
       FileCache::CACHE_TYPE_PERSISTENT);
 }
 
 }  // namespace internal
 }  // namespace drive