Add API to get a folder's size.

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

Index: chrome/browser/chromeos/extensions/file_manager/private_api_file_system.h
diff --git a/chrome/browser/chromeos/extensions/file_manager/private_api_file_system.h b/chrome/browser/chromeos/extensions/file_manager/private_api_file_system.h
index af65f69fa13a50f4c3debff3d3044ee3ef6cba05..300a6b7847bbeeacbea8e3f78f4294fe1a695e8f 100644
--- a/chrome/browser/chromeos/extensions/file_manager/private_api_file_system.h
+++ b/chrome/browser/chromeos/extensions/file_manager/private_api_file_system.h
@@ -336,6 +336,23 @@ class FileManagerPrivateInternalSetEntryTagFunction
   DISALLOW_COPY_AND_ASSIGN(FileManagerPrivateInternalSetEntryTagFunction);
 };
 
+// Implements the chrome.fileManagerPrivate.getDirectorySize mothod.
+class FileManagerPrivateInternalGetDirectorySizeFunction
+    : public LoggedAsyncExtensionFunction {
+ public:
+  FileManagerPrivateInternalGetDirectorySizeFunction();
+  DECLARE_EXTENSION_FUNCTION("fileManagerPrivateInternal.getDirectorySize",
+                             FILEMANAGERPRIVATEINTERNAL_GETDIRECTORYSIZE)
+
+ protected:
+  ~FileManagerPrivateInternalGetDirectorySizeFunction() override {}
+  // AsyncExtensionFunction overrides
+  bool RunAsync() override;
+
+ private:
+  const ChromeExtensionFunctionDetails chrome_details_;
+};
+
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_CHROMEOS_EXTENSIONS_FILE_MANAGER_PRIVATE_API_FILE_SYSTEM_H_