[Sync] Fix flakiness from Sessions refactor

components/sync_sessions/synced_session_tracker.cc

 // Copyright (c) 2012 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.
 
 #include "components/sync_sessions/synced_session_tracker.h"
 
 #include <utility>
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
@@ skipping 243 matching lines @@
   // rely on the later update to build the mapping (or a restart).
   GetTab(session_tag, tab_id);
 
   // The tab should be unmapped.
   std::unique_ptr<sessions::SessionTab> tab;
   auto it = unmapped_tabs_[session_tag].find(tab_id);
   if (it != unmapped_tabs_[session_tag].end()) {
     tab = std::move(it->second);
     unmapped_tabs_[session_tag].erase(it);
   }
-  DCHECK(tab);
+  if (!tab) {
+    LOG(ERROR) << "crbug.com/665196 Attempting to map tab " << tab_id

[skym, 2016/12/09 15:40:00]

This doesn't seem like the right bug number.

[Nicolas Zea, 2016/12/09 17:33:36]

Oops! Fixed

+               << " multiple times!";
+    return;
+  }
 
   tab->window_id.set_id(window_id);
   DVLOG(1) << "  - tab " << tab_id << " added to window " << window_id;
   DCHECK(GetSession(session_tag)->windows.find(window_id) !=
          GetSession(session_tag)->windows.end());
   auto& window_tabs = GetSession(session_tag)->windows[window_id]->tabs;
   if (window_tabs.size() <= tab_index) {
     window_tabs.resize(tab_index + 1);
   }
   DCHECK(!window_tabs[tab_index]);
@@ skipping 136 matching lines @@
   // Get rid of our convenience maps (does not delete the actual Window/Tabs
   // themselves; they should have all been deleted above).
   synced_window_map_.clear();
   synced_tab_map_.clear();
 
   local_tab_pool_.Clear();
   local_session_tag_.clear();
 }
 
 }  // namespace sync_sessions