[Sync] Replacing NULL with nullptr in code and null in comments for components/sync/

components/sync/base/enum_set.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 COMPONENTS_SYNC_BASE_ENUM_SET_H_
 #define COMPONENTS_SYNC_BASE_ENUM_SET_H_
 
 #include <bitset>
 #include <cstddef>
 #include <string>
@@ skipping 59 matching lines @@
   // /* ERROR */
   // for (EnumSet<...>::Iterator it = SomeFun().First(); ...
   //
   // Also, there are no guarantees as to what will happen if you
   // modify an EnumSet while traversing it with an iterator.
   class Iterator {
    public:
     // A default-constructed iterator can't do anything except check
     // Good().  You need to call First() on an EnumSet to get a usable
     // iterator.
-    Iterator() : enums_(NULL), i_(kValueCount) {}
+    Iterator() : enums_(nullptr), i_(kValueCount) {}
     ~Iterator() {}
 
     // Copy constructor and assignment welcome.
 
     // Returns true iff the iterator points to an EnumSet and it
     // hasn't yet traversed the EnumSet entirely.
     bool Good() const { return enums_ && i_ < kValueCount && enums_->test(i_); }
 
     // Returns the value the iterator currently points to.  Good()
     // must hold.
@@ skipping 163 matching lines @@
 
 template <typename E, E Min, E Max>
 EnumSet<E, Min, Max> Difference(EnumSet<E, Min, Max> set1,
                                 EnumSet<E, Min, Max> set2) {
   return EnumSet<E, Min, Max>(set1.enums_ & ~set2.enums_);
 }
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_BASE_ENUM_SET_H_