Get signals working in the EXTRA_DATA section of MHTML

chrome/browser/android/offline_pages/prerendering_offliner.cc

Index: chrome/browser/android/offline_pages/prerendering_offliner.cc
diff --git a/chrome/browser/android/offline_pages/prerendering_offliner.cc b/chrome/browser/android/offline_pages/prerendering_offliner.cc
index a6564ad078d662af7b164c009e039d8dd89aa383..d039867f8c8f0a30007c856da86b49d5147c671d 100644
--- a/chrome/browser/android/offline_pages/prerendering_offliner.cc
+++ b/chrome/browser/android/offline_pages/prerendering_offliner.cc
@@ -15,9 +15,14 @@
 #include "components/offline_pages/core/client_namespace_constants.h"
 #include "components/offline_pages/core/downloads/download_ui_adapter.h"
 #include "components/offline_pages/core/offline_page_model.h"
+#include "content/browser/download/mhtml_generation_manager.h"
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/web_contents.h"
 
+namespace {
+const char kApplicationJson[] = "application/json";
+}  // namespace
+
 namespace offline_pages {
 
 PrerenderingOffliner::PrerenderingOffliner(
@@ -83,6 +88,18 @@ void PrerenderingOffliner::OnLoadPageDone(
     else if (save_page_params.url != request.url())
       save_page_params.original_url = request.url();
 
+    std::string signal_string = SerializeLoadingSignalData();
+
+    // Attach a signal data section to the web contents.
+    content::MHTMLGenerationManager::MHTMLExtraSection signal_section;
+    signal_section.body = SerializeLoadingSignalData();
+    signal_section.content_type = kApplicationJson;
+    signal_section.content_location = "cid:signal-data-" +
+                                      std::to_string(request.request_id()) +
+                                      "@mhtml.blink";
+    content::MHTMLGenerationManager::MHTMLExtraData::AddToWebContents(
+        web_contents, signal_section);
+
     SavePage(save_page_params, std::move(archiver),
              base::Bind(&PrerenderingOffliner::OnSavePageDone,
                         weak_ptr_factory_.GetWeakPtr(), request));
@@ -94,6 +111,19 @@ void PrerenderingOffliner::OnLoadPageDone(
   }
 }
 
+std::string PrerenderingOffliner::SerializeLoadingSignalData() {
+  // Write the signal data into a single string.
+  std::string signal_string;
+  const std::vector<std::string>& signals = loader_->GetLoadingSignalData();
+
+  // TODO(petewil): Convert this to JSON, use json_writer.h
+  for (std::string signal : signals) {
+    signal_string += signal;
+    signal_string += "\r\n";
+  }
+  return signal_string;
+}
+
 void PrerenderingOffliner::OnSavePageDone(
     const SavePageRequest& request,
     SavePageResult save_result,