Add extra headers argument so we don't pass headers in the body.

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 db341ef4c87b63951480215df3ff2f69ab5334b3..6cd3803e3bb77873554c0771158f63958dd15d37 100644
--- a/chrome/browser/android/offline_pages/prerendering_offliner.cc
+++ b/chrome/browser/android/offline_pages/prerendering_offliner.cc
@@ -94,10 +94,10 @@ void PrerenderingOffliner::OnLoadPageDone(
 
     if (IsOfflinePagesLoadSignalCollectingEnabled()) {
       // Stash loading signals for writing when we write out the MHTML.
-      std::string headers =
-          base::StringPrintf("%s\r\n%s\r\n\r\n", kContentTransferEncodingBinary,
-                             kXHeaderForSignals);
-      std::string body = headers + SerializeLoadingSignalData();
+      // TODO(petewil): Add this data to the BackgroundLoaderOffliner too.
+      std::string extra_headers = base::StringPrintf(
+          "%s\r\n%s", kContentTransferEncodingBinary, kXHeaderForSignals);
+      std::string body = SerializeLoadingSignalData();
       std::string content_type = kContentType;
       std::string content_location = base::StringPrintf(
           "cid:signal-data-%" PRId64 "@mhtml.blink", request.request_id());
@@ -106,7 +106,8 @@ void PrerenderingOffliner::OnLoadPageDone(
           content::MHTMLExtraParts::FromWebContents(web_contents);
       DCHECK(extra_parts);
       if (extra_parts != nullptr) {
-        extra_parts->AddExtraMHTMLPart(content_type, content_location, body);
+        extra_parts->AddExtraMHTMLPart(content_type, content_location,
+                                       extra_headers, body);
       }
     }