Add is_srcdoc to FrameNavigationEntry and restore about::srcdoc URL.

content/browser/frame_host/frame_navigation_entry.cc

Index: content/browser/frame_host/frame_navigation_entry.cc
diff --git a/content/browser/frame_host/frame_navigation_entry.cc b/content/browser/frame_host/frame_navigation_entry.cc
index 5ebb6c29047d87e5ead0d369657015af217d22db..02b487bd10fc15172b1cbf4af9b2fc672422c539 100644
--- a/content/browser/frame_host/frame_navigation_entry.cc
+++ b/content/browser/frame_host/frame_navigation_entry.cc
@@ -23,7 +23,8 @@ FrameNavigationEntry::FrameNavigationEntry(
     const GURL& url,
     const Referrer& referrer,
     const std::string& method,
-    int64_t post_id)
+    int64_t post_id,
+    bool is_srcdoc)
     : frame_unique_name_(frame_unique_name),
       item_sequence_number_(item_sequence_number),
       document_sequence_number_(document_sequence_number),
@@ -32,7 +33,8 @@ FrameNavigationEntry::FrameNavigationEntry(
       url_(url),
       referrer_(referrer),
       method_(method),
-      post_id_(post_id) {}
+      post_id_(post_id),
+      is_srcdoc_(is_srcdoc) {}
 
 FrameNavigationEntry::~FrameNavigationEntry() {
 }
@@ -44,7 +46,7 @@ FrameNavigationEntry* FrameNavigationEntry::Clone() const {
   copy->UpdateEntry(frame_unique_name_, item_sequence_number_,
                     document_sequence_number_, site_instance_.get(), nullptr,
                     url_, referrer_, redirect_chain_, page_state_, method_,
-                    post_id_);
+                    post_id_, is_srcdoc_);
   return copy;
 }
 
@@ -59,7 +61,8 @@ void FrameNavigationEntry::UpdateEntry(
     const std::vector<GURL>& redirect_chain,
     const PageState& page_state,
     const std::string& method,
-    int64_t post_id) {
+    int64_t post_id,
+    bool is_srcdoc) {
   frame_unique_name_ = frame_unique_name;
   item_sequence_number_ = item_sequence_number;
   document_sequence_number_ = document_sequence_number;
@@ -71,6 +74,7 @@ void FrameNavigationEntry::UpdateEntry(
   page_state_ = page_state;
   method_ = method;
   post_id_ = post_id;
+  is_srcdoc_ = is_srcdoc;
 }
 
 void FrameNavigationEntry::set_item_sequence_number(