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

content/common/download/mhtml_save_status.cc

Index: content/common/download/mhtml_save_status.cc
diff --git a/content/common/download/mhtml_save_status.cc b/content/common/download/mhtml_save_status.cc
new file mode 100644
index 0000000000000000000000000000000000000000..e6cea2ab761997090e5f3b119ba6ae2feda43db9
--- /dev/null
+++ b/content/common/download/mhtml_save_status.cc
@@ -0,0 +1,32 @@
+// 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.
+
+#include "content/common/download/mhtml_save_status.h"
+
+#include "base/logging.h"
+
+namespace content {
+
+const char* GetMhtmlSaveStatusLabel(MhtmlSaveStatus save_status) {
+  switch (save_status) {
+    case MhtmlSaveStatus::SUCCESS:
+      return "Success";
+    case MhtmlSaveStatus::FILE_CLOSING_ERROR:
+      return "File closing error";
+    case MhtmlSaveStatus::FILE_CREATION_ERROR:
+      return "File creation error";
+    case MhtmlSaveStatus::FILE_WRITTING_ERROR:
+      return "File writing error";
+    case MhtmlSaveStatus::FRAME_NO_LONGER_EXISTS:
+      return "Frame no longer exists";
+    case MhtmlSaveStatus::FRAME_SERIALIZATION_FORBIDDEN:
+      return "Main frame serialization forbidden";
+    case MhtmlSaveStatus::RENDER_PROCESS_EXITED:
+      return "Render process no longer exists";
+  }
+  NOTREACHED();
+  return "<Invalid status>";
+}
+
+}  // namespace content