Improve DCHECK log to help in debugging its triggering

Small change to the DCHECK log I recently added to dump more and clearer
information about the snapshot.

Bug: 852616
Change-Id: I584f01d711bb885d6da2918d84c364059541843f
Reviewed-on: https://chromium-review.googlesource.com/1101975Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Carlos Knippschild <carlosk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567816}

chrome/browser/offline_pages/recent_tab_helper.cc

@@ -468,8 +468,9 @@ void RecentTabHelper::SavePageCallback(SnapshotProgressInfo* snapshot_info,
   DCHECK((snapshot_info->IsForLastN() &&
           snapshot_info->request_id == OfflinePageModel::kInvalidOfflineId) ||
          snapshot_info->request_id == offline_id)
-      << "IsForLastN: " << snapshot_info->IsForLastN()
-      << ", request_id: " << snapshot_info->request_id;
+      << "SnapshotProgressInfo: client_id=" << snapshot_info->client_id
+      << ", request_id=" << snapshot_info->request_id
+      << ", origin=" << snapshot_info->origin;
   // Store the assigned offline_id (for downloads case it will already contain
   // the same value).
   snapshot_info->request_id = offline_id;