Add API to get a folder's size.

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

 // 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.
 //
 // This file provides file system related API functions.
 
 #ifndef CHROME_BROWSER_CHROMEOS_EXTENSIONS_FILE_MANAGER_PRIVATE_API_FILE_SYSTEM_H_
 #define CHROME_BROWSER_CHROMEOS_EXTENSIONS_FILE_MANAGER_PRIVATE_API_FILE_SYSTEM_H_
 
 #include <stddef.h>
@@ skipping 318 matching lines @@
  private:
   const ChromeExtensionFunctionDetails chrome_details_;
 
   // Called when setting a tag is completed with either a success or an error.
   void OnSetEntryPropertyCompleted(drive::FileError result);
 
   ExtensionFunction::ResponseAction Run() override;
   DISALLOW_COPY_AND_ASSIGN(FileManagerPrivateInternalSetEntryTagFunction);
 };
 
+// Implements the chrome.fileManagerPrivate.getDirectorySize method.
+class FileManagerPrivateInternalGetDirectorySizeFunction
+    : public LoggedAsyncExtensionFunction {
+ public:
+  DECLARE_EXTENSION_FUNCTION("fileManagerPrivateInternal.getDirectorySize",
+                             FILEMANAGERPRIVATEINTERNAL_GETDIRECTORYSIZE)
+
+ protected:
+  ~FileManagerPrivateInternalGetDirectorySizeFunction() override {}
+
+  void OnDirectorySizeRetrieved(int64_t size);
+
+  // AsyncExtensionFunction overrides
+  bool RunAsync() override;
+};
+
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_CHROMEOS_EXTENSIONS_FILE_MANAGER_PRIVATE_API_FILE_SYSTEM_H_