Persist offline page info in a navigation entry if needed

components/sessions/core/serialized_navigation_entry.h

Index: components/sessions/core/serialized_navigation_entry.h
diff --git a/components/sessions/core/serialized_navigation_entry.h b/components/sessions/core/serialized_navigation_entry.h
index cc3b53d0f29df4d1cca140c959c8aa9b0c3f112e..f32b578cd1643223fea0e6eeb74ede83d0063d25 100644
--- a/components/sessions/core/serialized_navigation_entry.h
+++ b/components/sessions/core/serialized_navigation_entry.h
@@ -123,6 +123,11 @@ class SESSIONS_EXPORT SerializedNavigationEntry {
   }
   const std::vector<GURL>& redirect_chain() const { return redirect_chain_; }
 
+  // Defines the custom behavior to load the offline page if it exists. This is
+  // extracted from the extra request header "X-Chrome-offline" whose value is
+  // a comma/space separated name-value pair.
+  const std::string& offline_page_info() const { return offline_page_info_; }

[sky, 2016/09/13 01:53:31]

Why do we want to persist this as a string rather than something more
meaningful? Enum for example?

[jianli, 2016/09/13 20:29:18]

We have more than one properties needed to persist, like reason and id. In the
future, we might want to add some more properties.

[sky, 2016/09/13 23:30:42]

The down side of a string is that it's easy to miss an incompatible change and
not realize the effects that may have. A real structure/enum is easier to see
changes in and realize what the effects may be.

[jianli, 2016/09/13 23:44:16]

How do we want to persist the struct? Do we still want to serialize the struct
into a string and then persist it? 

I can move OfflinePageHeader struct out of offline_page_request_job.cc and use
it here. But I still need to build OfflinePageHeader struct from extra request
header in ContentSerializedNavigationBuilder::FromNavigationEntry.

+
  private:
   friend class ContentSerializedNavigationBuilder;
   friend class ContentSerializedNavigationDriver;
@@ -151,6 +156,7 @@ class SESSIONS_EXPORT SerializedNavigationEntry {
   int http_status_code_;
   bool is_restored_;    // Not persisted.
   std::vector<GURL> redirect_chain_;  // Not persisted.
+  std::string offline_page_info_;  // Not synced.
 
   // Additional information.
   BlockedState blocked_state_;