Get signals working in the EXTRA_DATA section of MHTML

content/browser/download/mhtml_generation_manager.h

Index: content/browser/download/mhtml_generation_manager.h
diff --git a/content/browser/download/mhtml_generation_manager.h b/content/browser/download/mhtml_generation_manager.h
index e30001535b03735758e09f2734d69ce5cd1c03d7..66c9e405964355c2c92f2f30f5fdde4f68d83537 100644
--- a/content/browser/download/mhtml_generation_manager.h
+++ b/content/browser/download/mhtml_generation_manager.h
@@ -15,7 +15,9 @@
 #include "base/macros.h"
 #include "base/memory/singleton.h"
 #include "base/process/process.h"
+#include "base/supports_user_data.h"
 #include "content/common/download/mhtml_save_status.h"
+#include "content/public/browser/web_contents.h"
 #include "content/public/common/mhtml_generation_params.h"
 #include "ipc/ipc_platform_file.h"
 
@@ -34,7 +36,7 @@ class WebContents;
 // MHTMLGenerationManager is a singleton.  Each call to SaveMHTML method creates
 // a new instance of MHTMLGenerationManager::Job that tracks generation of a
 // single MHTML file.
-class MHTMLGenerationManager {
+class CONTENT_EXPORT MHTMLGenerationManager {
  public:
   static MHTMLGenerationManager* GetInstance();
 
@@ -58,6 +60,39 @@ class MHTMLGenerationManager {
       const std::set<std::string>& digests_of_uris_of_serialized_resources,
       base::TimeDelta renderer_main_thread_time);
 
+  // Contained class that represents an extra data part.  With the addition of
+  // the MHTMLExtraData class, we can add enough information to create an extra
+  // MHTML part to be added into the complete file.  For instance, this might
+  // be used for gathering load time signals in debug code for analysis, but
+  // the mechanism is fairly general, and could be used to add arbitrary parts.
+  // Specify the content type, content location, and body, and the methods in
+  // MHTMLExtraData will do the rest.
+  struct MHTMLExtraPart {
+    std::string content_type;
+    std::string content_location;
+    std::string body;
+  };
+
+  // Helper class to put extra parts into the WebContents user data, and take
+  // them back out again.
+  class MHTMLExtraData : public base::SupportsUserData::Data {
+   public:
+    MHTMLExtraData();
+    ~MHTMLExtraData() override;
+
+    // Get the data string out of the web contents. The web contents retains
+    // ownership of the vector.  Returns nullptr if none found.
+    static std::vector<MHTMLExtraPart>* FromWebContents(
+        content::WebContents* contents);
+
+    // Add the extra part to the data structure stored by the WebContents.
+    static void AddPartToWebContents(content::WebContents* contents,
+                                     MHTMLExtraPart& part);
+
+   private:
+    std::vector<MHTMLExtraPart> parts_;
+  };
+
  private:
   friend struct base::DefaultSingletonTraits<MHTMLGenerationManager>;
   class Job;