[SyncFS] Check SyncEngine's availability

chrome/browser/sync_file_system/drive_backend/sync_engine.cc

 // Copyright 2013 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 "chrome/browser/sync_file_system/drive_backend/sync_engine.h"
 
 #include <vector>
 
 #include "base/bind.h"
 #include "base/metrics/histogram.h"
@@ skipping 53 matching lines @@
  public:
   WorkerObserver(base::SequencedTaskRunner* ui_task_runner,
                  base::WeakPtr<SyncEngine> sync_engine)
       : ui_task_runner_(ui_task_runner),
         sync_engine_(sync_engine) {}
 
   virtual ~WorkerObserver() {}
 
   virtual void OnPendingFileListUpdated(int item_count) OVERRIDE {
     if (ui_task_runner_->RunsTasksOnCurrentThread()) {
-      sync_engine_->OnPendingFileListUpdated(item_count);
+      if (sync_engine_)
+        sync_engine_->OnPendingFileListUpdated(item_count);
       return;
     }
 
     ui_task_runner_->PostTask(
         FROM_HERE,
         base::Bind(&SyncEngine::OnPendingFileListUpdated,
                    sync_engine_,
                    item_count));
   }
 
   virtual void OnFileStatusChanged(const fileapi::FileSystemURL& url,
                                    SyncFileStatus file_status,
                                    SyncAction sync_action,
                                    SyncDirection direction) OVERRIDE {
     if (ui_task_runner_->RunsTasksOnCurrentThread()) {
-      sync_engine_->OnFileStatusChanged(
-          url, file_status, sync_action, direction);
+      if (sync_engine_)
+        sync_engine_->OnFileStatusChanged(
+            url, file_status, sync_action, direction);
       return;
     }
 
     ui_task_runner_->PostTask(
         FROM_HERE,
         base::Bind(&SyncEngine::OnFileStatusChanged,
                    sync_engine_,
                    url, file_status, sync_action, direction));
   }
 
   virtual void UpdateServiceState(RemoteServiceState state,
                                   const std::string& description) OVERRIDE {
     if (ui_task_runner_->RunsTasksOnCurrentThread()) {
-      sync_engine_->UpdateServiceState(state, description);
+      if (sync_engine_)
+        sync_engine_->UpdateServiceState(state, description);
       return;
     }
 
     ui_task_runner_->PostTask(
         FROM_HERE,
         base::Bind(&SyncEngine::UpdateServiceState,
                    sync_engine_, state, description));
   }
 
  private:
@@ skipping 434 matching lines @@
         tracker.tracker_kind() == TRACKER_KIND_APP_ROOT;
     if (is_app_enabled && !is_app_root_tracker_enabled)
       EnableOrigin(origin, base::Bind(&EmptyStatusCallback));
     else if (!is_app_enabled && is_app_root_tracker_enabled)
       DisableOrigin(origin, base::Bind(&EmptyStatusCallback));
   }
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system