Revert "Remove old serializer" It caused a regression, crbug.com/510422

public/web/WebPageSerializer.h

Index: public/web/WebPageSerializer.h
diff --git a/public/web/WebPageSerializer.h b/public/web/WebPageSerializer.h
index 97359624a9b1490c3aa827a942d995c9255e5ea9..333e010eb44f82ca52d41b088c2c20b9690bc3eb 100644
--- a/public/web/WebPageSerializer.h
+++ b/public/web/WebPageSerializer.h
@@ -97,6 +97,14 @@ public:
         const WebVector<WebString>& localPaths,
         const WebString& localDirectoryName);
 
+    // Retrieve all the resource for the passed view, including the main frame
+    // and sub-frames. Returns true if all resources were retrieved
+    // successfully.
+    BLINK_EXPORT static bool retrieveAllResources(WebView*,
+                                                   const WebVector<WebCString>& supportedSchemes,
+                                                   WebVector<WebURL>* resources,
+                                                   WebVector<WebURL>* frames);
+
     // FIXME: The following are here for unit testing purposes. Consider
     // changing the unit tests instead.