FileAPI: Factor out getting root URI and FS name parts into each FS backend

chrome/browser/chromeos/fileapi/file_system_backend.cc

Index: chrome/browser/chromeos/fileapi/file_system_backend.cc
diff --git a/chrome/browser/chromeos/fileapi/file_system_backend.cc b/chrome/browser/chromeos/fileapi/file_system_backend.cc
index 148e148dd396e9b34eff31665bc14c9eb2301041..4790e08679438e1781dfb64dab0dfdc9e348fb60 100644
--- a/chrome/browser/chromeos/fileapi/file_system_backend.cc
+++ b/chrome/browser/chromeos/fileapi/file_system_backend.cc
@@ -113,7 +113,9 @@ void FileSystemBackend::OpenFileSystem(
     const OpenFileSystemCallback& callback) {
   DCHECK(fileapi::IsolatedContext::IsIsolatedType(type));
   // Nothing to validate for external filesystem.
-  callback.Run(base::PLATFORM_FILE_OK);
+  callback.Run(GetFileSystemRootURI(origin_url, type),
+               GetFileSystemName(origin_url, type),
+               base::PLATFORM_FILE_OK);
 }
 
 fileapi::FileSystemQuotaUtil* FileSystemBackend::GetQuotaUtil() {