Moved ScopeStopObserving to a template class in change_processor.h.

chrome/browser/sync/glue/change_processor.h

 // Copyright (c) 2011 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.
 
 #ifndef CHROME_BROWSER_SYNC_GLUE_CHANGE_PROCESSOR_H_
 #define CHROME_BROWSER_SYNC_GLUE_CHANGE_PROCESSOR_H_
 #pragma once
 
 #include "chrome/browser/sync/engine/syncapi.h"
 #include "chrome/browser/sync/glue/sync_backend_host.h"
@@ skipping 34 matching lines @@
 
   // The changes found in ApplyChangesFromSyncModel may be too slow to be
   // performed while holding a [Read/Write]Transaction lock or may interact
   // with another thread, which might itself be waiting on the transaction lock,
   // putting us at risk of deadlock.
   // This function is called once the transactional lock is released and it is
   // safe to perform inter-thread or slow I/O operations. Note that not all
   // datatypes need this, so we provide an empty default version.
   virtual void CommitChangesFromSyncModel();
 
+  // This ensures that startobserving gets called after stopobserving even
+  // if there is an early return in the function.
+  template <class T>
+  class ScopedStopObserving {
+   public:
+    explicit ScopedStopObserving(T* processor)
+        : processor_(processor) {
+      processor_->StopObserving();
+    }
+    ~ScopedStopObserving() {
+      processor_->StartObserving();
+    }
+
+   private:
+    ScopedStopObserving() {}
+    T* processor_;
+  };
+
  protected:
   // These methods are invoked by Start() and Stop() to do
   // implementation-specific work.
   virtual void StartImpl(Profile* profile) = 0;
   virtual void StopImpl() = 0;
 
   bool running() { return running_; }
   UnrecoverableErrorHandler* error_handler();
   virtual sync_api::UserShare* share_handle();
 
  private:
   bool running_;  // True if we have been told it is safe to process changes.
   UnrecoverableErrorHandler* error_handler_;  // Guaranteed to outlive us.
 
   // The sync model we are processing changes from. Non-NULL when |running_| is
   // true.
   sync_api::UserShare* share_handle_;
 
   DISALLOW_COPY_AND_ASSIGN(ChangeProcessor);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_GLUE_CHANGE_PROCESSOR_H_