Update from https://crrev.com/327068

base/observer_list_unittest.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 "base/observer_list.h"
 #include "base/observer_list_threadsafe.h"
 
 #include <vector>
 
 #include "base/compiler_specific.h"
@@ skipping 53 matching lines @@
 
 template <typename ObserverListType>
 class AddInObserve : public Foo {
  public:
   explicit AddInObserve(ObserverListType* observer_list)
       : added(false),
         observer_list(observer_list),
         adder(1) {
   }
 
-  virtual void Observe(int x) override {
+  void Observe(int x) override {
     if (!added) {
       added = true;
       observer_list->AddObserver(&adder);
     }
   }
 
   bool added;
   ObserverListType* observer_list;
   Adder adder;
 };
 
 
 static const int kThreadRunTime = 2000;  // ms to run the multi-threaded test.
 
 // A thread for use in the ThreadSafeObserver test
 // which will add and remove itself from the notification
 // list repeatedly.
 class AddRemoveThread : public PlatformThread::Delegate,
                         public Foo {
  public:
   AddRemoveThread(ObserverListThreadSafe<Foo>* list, bool notify)
       : list_(list),
-        loop_(NULL),
+        loop_(nullptr),
         in_list_(false),
         start_(Time::Now()),
         count_observes_(0),
         count_addtask_(0),
         do_notifies_(notify),
         weak_factory_(this) {
   }
 
   ~AddRemoveThread() override {}
 
@@ skipping 426 matching lines @@
   ListDestructor a(observer_list);
   observer_list->AddObserver(&a);
 
   FOR_EACH_OBSERVER(Foo, *observer_list, Observe(0));
   // If this test fails, there'll be Valgrind errors when this function goes out
   // of scope.
 }
 
 }  // namespace
 }  // namespace base