Refactor the offline page storage to include client namespace and id.

components/offline_pages/proto/offline_pages.proto

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Offline page item protocol for storage and exchanging of offline page
 // metadata.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 option retain_unknown_fields = true;
 
 package offline_pages;
 
 message OfflinePageEntry {
   // URL of the offline page.
-  required string url = 1;
+  optional string url = 1;
 
   // Bookmark ID of the offline page.
-  required int64 bookmark_id = 2;
+  optional int64 deprecated_bookmark_id = 2;

[fgorski, 2016/02/23 17:15:31]

specify default to -1 as that is the invalid bookmark id, per:
https://code.google.com/p/chromium/codesearch#chromium/src/chrome/android/jav...

[bburns, 2016/02/23 19:25:39]

Done.

+
+  // Offline ID of the page.  Offline ID has replaced Bookmark ID as the primary key
+  optional int64 offline_id = 10;
 
   // Version of the offline page metadata.
-  required int32 version = 3;
+  optional int32 version = 3;
 
   // Path to the offline archive.
-  required string file_path = 4;
+  optional string file_path = 4;
 
   // Size of the offline archive.
   optional int64 file_size = 5;
 
   // Creation time of the offline archive.
   optional int64 creation_time = 6;
 
   // Last access time of the offline archive.
   optional int64 last_access_time = 7;
 
   // Number of times that the offline archive has been accessed.
   optional int32 access_count = 8;
 
   // Flags about the state and behavior of the offline page.
   enum Flags {
     // No flag is set.
     NONE = 0;
     // Indicates that the page is marked for deletion. The real deletion will
     // occur soon, after which the undo will not be possible.
     MARKED_FOR_DELETION = 1;
   };
 
   // Flags for the offline page.
   optional Flags flags = 9;
+
+  // Information about this offline page in the namespace/id of the client that
+  // requested that it be saved. Useful for reverse lookups.
+  optional string client_id_name_space = 11;
+  optional string client_id = 12;
 }