[fsp] Add an option for mounting in R/W mode.

chrome/browser/chromeos/extensions/file_system_provider/file_system_provider_api.cc

Index: chrome/browser/chromeos/extensions/file_system_provider/file_system_provider_api.cc
diff --git a/chrome/browser/chromeos/extensions/file_system_provider/file_system_provider_api.cc b/chrome/browser/chromeos/extensions/file_system_provider/file_system_provider_api.cc
index 09e430a0e9cb241d741e0a5873128df29296f845..f8753a9724a77df1a84d17b90206e3c4ca01f69f 100644
--- a/chrome/browser/chromeos/extensions/file_system_provider/file_system_provider_api.cc
+++ b/chrome/browser/chromeos/extensions/file_system_provider/file_system_provider_api.cc
@@ -52,7 +52,8 @@ bool FileSystemProviderMountFunction::RunSync() {
   // TODO(mtomasz): Pass more detailed errors, rather than just a bool.
   if (!service->MountFileSystem(extension_id(),
                                 params->options.file_system_id,
-                                params->options.display_name)) {
+                                params->options.display_name,
+                                params->options.writable)) {
     base::ListValue* result = new base::ListValue();
     result->Append(CreateError(kSecurityErrorName, kMountFailedErrorMessage));
     SetResult(result);