[fsp] Add support for opening files.

chrome/browser/chromeos/file_system_provider/fake_provided_file_system.cc

Index: chrome/browser/chromeos/file_system_provider/fake_provided_file_system.cc
diff --git a/chrome/browser/chromeos/file_system_provider/fake_provided_file_system.cc b/chrome/browser/chromeos/file_system_provider/fake_provided_file_system.cc
index f27aeb01fb4ad1f32c00f6802c0a272a72cf68fd..aab2a8310d14f352024dcf890f1122d6e21c9dc5 100644
--- a/chrome/browser/chromeos/file_system_provider/fake_provided_file_system.cc
+++ b/chrome/browser/chromeos/file_system_provider/fake_provided_file_system.cc
@@ -118,6 +118,20 @@ void FakeProvidedFileSystem::ReadDirectory(
   }
 }
 
+void FakeProvidedFileSystem::OpenFile(
+    const base::FilePath& file_path,
+    OpenFileMode mode,
+    bool create,
+    const fileapi::AsyncFileUtil::StatusCallback& callback) {
+  if (file_path.AsUTF8Unsafe() != "/hello.txt" ||
+      mode == OPEN_FILE_MODE_WRITE || create) {
+    callback.Run(base::File::FILE_ERROR_SECURITY);
+    return;
+  }
+
+  callback.Run(base::File::FILE_OK);
+}
+
 const ProvidedFileSystemInfo& FakeProvidedFileSystem::GetFileSystemInfo()
     const {
   return file_system_info_;