Get signals working in the EXTRA_DATA section of MHTML

content/public/common/mhtml_generation_params.h

Index: content/public/common/mhtml_generation_params.h
diff --git a/content/public/common/mhtml_generation_params.h b/content/public/common/mhtml_generation_params.h
index f4e5bd8f727b277928f9be9a69ca53bc0cf28826..3efd48838dc690caebe5a001ccbf886a9a37a260 100644
--- a/content/public/common/mhtml_generation_params.h
+++ b/content/public/common/mhtml_generation_params.h
@@ -5,6 +5,9 @@
 #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"
@@ -13,7 +16,11 @@ 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;
@@ -31,6 +38,11 @@ struct CONTENT_EXPORT MHTMLGenerationParams {
 
   // 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