Allow Offline MHTML save operations to succeed even with missing frames.

content/public/common/mhtml_generation_params.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_PUBLIC_COMMON_MHTML_GENERATION_PARAMS_H_
 #define CONTENT_PUBLIC_COMMON_MHTML_GENERATION_PARAMS_H_
 
 #include "base/files/file_path.h"
 #include "content/common/content_export.h"
 #include "third_party/WebKit/public/web/WebFrameSerializerCacheControlPolicy.h"
@@ skipping 10 matching lines @@
   // Uses Content-Transfer-Encoding: binary when encoding.  See
   // https://tools.ietf.org/html/rfc2045 for details about
   // Content-Transfer-Encoding.
   bool use_binary_encoding = false;
 
   // By default, MHTML includes all subresources.  This flag can be used to
   // cause the generator to fail or silently ignore resources if the
   // Cache-Control header is used.
   blink::WebFrameSerializerCacheControlPolicy cache_control_policy =
       blink::WebFrameSerializerCacheControlPolicy::None;
+
+  // This setting defaults to |false|. If set to |true| it allows the saving
+  // operation to still succeed even when frames go missing during the saving
+  // process (with the obvious exception of the main frame).
+  bool ignore_missing_frames = false;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_COMMON_MHTML_GENERATION_PARAMS_H_