Revert of Remove about:srcdoc url conversion.

content/renderer/render_frame_impl.cc

Index: content/renderer/render_frame_impl.cc
diff --git a/content/renderer/render_frame_impl.cc b/content/renderer/render_frame_impl.cc
index ea987b3bda0c70e50ef023d6d10ca131dedced1c..00f17b47be2c3ea857ea9936a7d166eba36af23f 100644
--- a/content/renderer/render_frame_impl.cc
+++ b/content/renderer/render_frame_impl.cc
@@ -4810,6 +4810,8 @@
   params.item_sequence_number = item.itemSequenceNumber();
   params.document_sequence_number = item.documentSequenceNumber();
 
+  params.is_srcdoc = params.url == content::kAboutSrcDocURL;
+
   // If the page contained a client redirect (meta refresh, document.loc...),
   // set the referrer appropriately.
   if (ds->isClientRedirect()) {