Update from https://crrev.com/328418

base/scoped_observer.h

 // 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.
 
 #ifndef BASE_SCOPED_OBSERVER_H_
 #define BASE_SCOPED_OBSERVER_H_
 
 #include <algorithm>
 #include <vector>
 
@@ skipping 30 matching lines @@
     for (size_t i = 0; i < sources_.size(); ++i)
       sources_[i]->RemoveObserver(observer_);
     sources_.clear();
   }
 
   bool IsObserving(Source* source) const {
     return std::find(sources_.begin(), sources_.end(), source) !=
         sources_.end();
   }
 
+  bool IsObservingSources() const { return !sources_.empty(); }
+
  private:
   Observer* observer_;
 
   std::vector<Source*> sources_;
 
   DISALLOW_COPY_AND_ASSIGN(ScopedObserver);
 };
 
 #endif  // BASE_SCOPED_OBSERVER_H_