gdata: Convert FindEntryByResourceIdSync() to asynchronous.

chrome/browser/chromeos/gdata/gdata_file_system.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/gdata/gdata_file_system.h"
 
 #include <errno.h>
 #include <sys/stat.h>
 
 #include <set>
@@ skipping 1023 matching lines @@
   update_timer_.Stop();
 }
 
 void GDataFileSystem::Authenticate(const AuthStatusCallback& callback) {
   // TokenFetcher, used in DocumentsService, must be run on UI thread.
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   documents_service_->Authenticate(callback);
 }
 
-void GDataFileSystem::FindEntryByResourceIdSync(
+void GDataFileSystem::FindEntryByResourceIdAsync(
     const std::string& resource_id,
     const FindEntryCallback& callback) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI) ||

[achuithb, 2012/06/11 20:46:37]

Not sure I understand the point of this DCHECK?

[hshi1, 2012/06/11 20:58:51]

This is essentially a copy & paste of the many other functions (such as
GetEntryInfoByPathAsync and ReadDirectoryByPathAsync). In principle it is not
necessary as the RunTaskOnUIThread ensures the task will be run on UI, but it
seems that we expect the entry to be called on UI or IO thread.

[achuithb, 2012/06/11 21:48:41]

I've not seen this pattern before (outside of this file). And in this particular
case it really does seem pointless since the only thing you do is schedule on
the UI thread. But you can leave it in for consistency.

+         BrowserThread::CurrentlyOn(BrowserThread::IO));
+  RunTaskOnUIThread(
+      base::Bind(&GDataFileSystem::FindEntryByResourceIdAsyncOnUIThread,
+                 ui_weak_ptr_,
+                 resource_id,
+                 CreateRelayCallback(callback)));
+}
+
+void GDataFileSystem::FindEntryByResourceIdAsyncOnUIThread(
+    const std::string& resource_id,
+    const FindEntryCallback& callback) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
   base::AutoLock lock(lock_);  // To access root.
-
   GDataFile* file = NULL;
   GDataEntry* entry = root_->GetEntryByResourceId(resource_id);
   if (entry)
     file = entry->AsGDataFile();
 
   if (file)
     callback.Run(base::PLATFORM_FILE_OK, file);
   else
     callback.Run(base::PLATFORM_FILE_ERROR_NOT_FOUND, NULL);
 }
@@ skipping 4132 matching lines @@
     base::PlatformFileError error,
     const std::string& resource_id,
     const std::string& md5) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   if (!callback.is_null())
     callback.Run(error);
 }
 
 }  // namespace gdata