[fsp] Add support for truncating files.

chrome/browser/chromeos/file_system_provider/fake_provided_file_system.cc

 // Copyright 2014 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/file_system_provider/fake_provided_file_system.h"
 
 #include <string>
 
 #include "base/files/file.h"
 #include "base/message_loop/message_loop_proxy.h"
@@ skipping 248 matching lines @@
 }
 
 void FakeProvidedFileSystem::MoveEntry(
     const base::FilePath& source_path,
     const base::FilePath& target_path,
     const fileapi::AsyncFileUtil::StatusCallback& callback) {
   base::MessageLoopProxy::current()->PostTask(
       FROM_HERE, base::Bind(callback, base::File::FILE_OK));
 }
 
+void FakeProvidedFileSystem::Truncate(
+    const base::FilePath& file_path,
+    int64 length,
+    const fileapi::AsyncFileUtil::StatusCallback& callback) {
+  base::MessageLoopProxy::current()->PostTask(
+      FROM_HERE, base::Bind(callback, base::File::FILE_OK));
+}
+
 const ProvidedFileSystemInfo& FakeProvidedFileSystem::GetFileSystemInfo()
     const {
   return file_system_info_;
 }
 
 RequestManager* FakeProvidedFileSystem::GetRequestManager() {
   NOTREACHED();
   return NULL;
 }
 
 ProvidedFileSystemInterface* FakeProvidedFileSystem::Create(
     Profile* profile,
     const ProvidedFileSystemInfo& file_system_info) {
   return new FakeProvidedFileSystem(file_system_info);
 }
 
 base::WeakPtr<ProvidedFileSystemInterface>
 FakeProvidedFileSystem::GetWeakPtr() {
   return weak_ptr_factory_.GetWeakPtr();
 }
 
 }  // namespace file_system_provider
 }  // namespace chromeos