Fail when saving page as MHTML provides information about the cause.

content/common/download/mhtml_save_status.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_COMMON_DOWNLOAD_MHTML_SAVE_STATUS_H_
+#define CONTENT_COMMON_DOWNLOAD_MHTML_SAVE_STATUS_H_
+
+namespace content {
+
+// Status result enum for MHTML generation.
+enum class MhtmlSaveStatus {
+  SUCCESS = 0,
+
+  // Could not properly close the file where data was written to. Determined by
+  // the browser.
+  FILE_CLOSING_ERROR,
+
+  // Could not create the file that would be written to. Determined by the
+  // browser.
+  FILE_CREATION_ERROR,
+
+  // Could not write serialized data to the file. Determined by the renderer.
+  FILE_WRITTING_ERROR,
+
+  // The DOM changed and a previously existing frame is no more. Determined by
+  // the browser.
+  FRAME_NO_LONGER_EXIST,

[Łukasz Anforowicz, 2016/11/22 19:22:13]

nit: FRAME_NO_LONGER_EXISTS

[carlosk, 2016/11/22 23:26:24]

Done.

+
+  // A frame was not allowed to be serialized by either policy or cache control.

[Łukasz Anforowicz, 2016/11/22 19:22:13]

nit: s/A frame/The main frame/ ?

[carlosk, 2016/11/22 23:26:23]

Done.

+  // Determined by the renderer.
+  FRAME_SERIALIZATION_FORBIDDEN,
+
+  // A render process needed for the serialization of one of the page's frame is
+  // no more. Determined by the browser.
+  RENDER_PROCESS_EXITED,
+
+  // NOTE: always keep this entry at the end. Add new result types only
+  // immediately above this line. Make sure to update the corresponding
+  // histogram enum accordingly.
+  STATUS_COUNT,
+};
+
+}  // namespace content
+
+#endif  // CONTENT_COMMON_DOWNLOAD_MHTML_SAVE_STATUS_H_