Get signals working in the EXTRA_DATA section of MHTML

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 <string>
+#include <vector>
+
 #include "base/files/file_path.h"
 #include "content/common/content_export.h"
 #include "third_party/WebKit/public/web/WebFrameSerializerCacheControlPolicy.h"
 
 namespace content {
 
 struct CONTENT_EXPORT MHTMLGenerationParams {
   MHTMLGenerationParams(const base::FilePath& file_path);
-  ~MHTMLGenerationParams() = default;
+
+  ~MHTMLGenerationParams();
+
+  // We need a copy constructor since we have a complex subtype.
+  MHTMLGenerationParams(const MHTMLGenerationParams& other);
 
   // The file that will contain the generated MHTML.
   base::FilePath file_path;
 
   // 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;
 
   // Removes popups that could obstruct the user's view of normal content.
   bool remove_popup_overlay = false;
+
+  // Extra data to be included when generating the MHTML - for example,
+  // logging the signals that were received before capturing this MHTML
+  // for background offlining.
+  std::vector<std::string> extra_data;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_COMMON_MHTML_GENERATION_PARAMS_H_