Implement PrerenderManager::AddPrerenderForOffline()

chrome/browser/prerender/prerender_manager.h

Index: chrome/browser/prerender/prerender_manager.h
diff --git a/chrome/browser/prerender/prerender_manager.h b/chrome/browser/prerender/prerender_manager.h
index c33c540657d6824793f8f84767a7b6c91f52eb00..0d5e385d4b2bc451e669f6eecd1ad76cccf93d5c 100644
--- a/chrome/browser/prerender/prerender_manager.h
+++ b/chrome/browser/prerender/prerender_manager.h
@@ -151,6 +151,12 @@ class PrerenderManager : public base::SupportsWeakPtr<PrerenderManager>,
       content::SessionStorageNamespace* session_storage_namespace,
       const gfx::Size& size);
 
+  // Adds a prerender from an external request that will always prerender.

[pasko, 2016/04/05 11:49:56]

This is not an "external request", calling it such is confusing (or maybe I
misunderstand the terminology).

Please add the comment from the doc as we discussed, some obvious stuff can be
stripped. My suggestion:

// Adds a prerender for the background loader. Returns a caller-owned
// PrerenderHandle* if the URL was added, NULL if it was not.
// 
// The caller may set an observer on the handle to receive load events. When the
// caller is done using the WebContents, it should call OnCancel() on the handle
// to free the resources associated with the prerender.
//
// The caller must provide two guarantees:
// 1. It must never ask to as for a swap-in;
// 2. The SessionStorageNamespace must not be shared with any tab / page load
//    to avoid swapping in from there.

[gabadie, 2016/04/05 13:35:24]

My bad. Done.

+  PrerenderHandle* AddPrerenderForOffline(
+      const GURL& url,
+      content::SessionStorageNamespace* session_storage_namespace,
+      const gfx::Size& size);
+
   // Cancels all active prerenders.
   void CancelAllPrerenders();