Add API to get a folder's size.

chrome/browser/chromeos/extensions/file_manager/private_api_file_system.cc

 // Copyright 2013 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/extensions/file_manager/private_api_file_system.h"
 
 #include <sys/statvfs.h>
 
 #include <algorithm>
 #include <set>
 #include <utility>
 #include <vector>
 
+#include "base/files/file_util.h"
 #include "base/memory/ptr_util.h"
 #include "base/memory/weak_ptr.h"
 #include "base/posix/eintr_wrapper.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/sys_info.h"
 #include "base/task_runner_util.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "chrome/browser/browser_process.h"
@@ skipping 924 matching lines @@
                  this));
   return RespondLater();
 }
 
 void FileManagerPrivateInternalSetEntryTagFunction::OnSetEntryPropertyCompleted(
     drive::FileError result) {
   Respond(result == drive::FILE_ERROR_OK ? NoArguments()
                                          : Error("Failed to set a tag."));
 }
 
+bool FileManagerPrivateInternalGetDirectorySizeFunction::RunAsync() {
+  using extensions::api::file_manager_private_internal::GetDirectorySize::
+      Params;
+  const std::unique_ptr<Params> params(Params::Create(*args_));
+  EXTENSION_FUNCTION_VALIDATE(params);
+
+  if (params->url.empty()) {
+    SetError("File URL must be provided");
+    return false;
+  }
+
+  const base::FilePath root_path = file_manager::util::GetLocalPathFromURL(
+      render_frame_host(), GetProfile(), GURL(params->url));
+
+  if (root_path.empty())
+    return false;
+
+  base::PostTaskAndReplyWithResult(
+      BrowserThread::GetBlockingPool(), FROM_HERE,
+      base::Bind(&base::ComputeDirectorySize,
+                 root_path),
+      base::Bind(&FileManagerPrivateInternalGetDirectorySizeFunction::
+                    OnDirectorySizeRetrieved, this));

[fukino, 2016/08/30 06:55:49]

This line's indent level looks incorrect. Could you try git cl format?

[harukam, 2016/08/30 07:35:38]

Thanks! Done.

+  return true;
+}
+
+void FileManagerPrivateInternalGetDirectorySizeFunction::
+    OnDirectorySizeRetrieved(int64_t size) {
+  SetResult(
+      base::MakeUnique<base::FundamentalValue>(static_cast<double>(size)));
+  SendResponse(true);
+}
+
 }  // namespace extensions