OpenFileSystem should accept not mount_type but lower filesystem type

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 0da8d357647e65efcf43beb3da29095a5dee5f65..33c3f6c69f12e1a86d6d78464b6fc829787b3266 100644
--- a/chrome/browser/chromeos/fileapi/file_system_backend.cc
+++ b/chrome/browser/chromeos/fileapi/file_system_backend.cc
@@ -109,10 +109,13 @@ void FileSystemBackend::OpenFileSystem(
     fileapi::FileSystemType type,
     fileapi::OpenFileSystemMode mode,
     const OpenFileSystemCallback& callback) {
-  DCHECK(fileapi::IsolatedContext::IsIsolatedType(type));
+  DCHECK(CanHandleType(type));
+  // TODO(nhiroki): Avoid this hard-coded mount type to support multiple
+  // filesystems (http://crbug.com/297412).
+  fileapi::FileSystemType mount_type = fileapi::kFileSystemTypeExternal;
   // Nothing to validate for external filesystem.
-  callback.Run(GetFileSystemRootURI(origin_url, type),
-               GetFileSystemName(origin_url, type),
+  callback.Run(GetFileSystemRootURI(origin_url, mount_type),
+               GetFileSystemName(origin_url, mount_type),
                base::PLATFORM_FILE_OK);
 }