Have the RequestCoordinator generate the offline_id

chrome/browser/android/offline_pages/prerendering_offliner.h

Index: chrome/browser/android/offline_pages/prerendering_offliner.h
diff --git a/chrome/browser/android/offline_pages/prerendering_offliner.h b/chrome/browser/android/offline_pages/prerendering_offliner.h
index 83d09d06b4add1aa5b7174ebfcaf19d8390b2c71..61e60d2e3829e7c74183c7391bdb50e665f991cd 100644
--- a/chrome/browser/android/offline_pages/prerendering_offliner.h
+++ b/chrome/browser/android/offline_pages/prerendering_offliner.h
@@ -53,6 +53,7 @@ class PrerenderingOffliner : public Offliner {
   // TODO(dougarnett): Consider making OfflinePageModel mockable instead.
   virtual void SavePage(const GURL& url,
                         const ClientId& client_id,
+                        int64_t offline_id,

[Dmitry Titov, 2016/08/16 02:25:00]

Naming suggestion: maybe proposed_offline_id? To capture the spirit that it is
optional, can be 0 which means no proposed or suggested id is passed in.

[Pete Williamson, 2016/08/16 18:54:56]

Done.

                         std::unique_ptr<OfflinePageArchiver> archiver,
                         const SavePageCallback& save_callback);