Update from https://crrev.com/329939

base/prefs/pref_registry.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_PREFS_PREF_REGISTRY_H_
 #define BASE_PREFS_PREF_REGISTRY_H_
 
 #include "base/containers/hash_tables.h"
 #include "base/memory/ref_counted.h"
 #include "base/prefs/base_prefs_export.h"
@@ skipping 14 matching lines @@
 // construction parameter to PrefService.
 //
 // Currently, registrations after constructing the PrefService will
 // also work, but this is being deprecated.
 class BASE_PREFS_EXPORT PrefRegistry : public base::RefCounted<PrefRegistry> {
  public:
   // Registration flags that can be specified which impact how the pref will
   // behave or be stored. This will be passed in a bitmask when the pref is
   // registered. Subclasses of PrefRegistry can specify their own flags. Care
   // must be taken to ensure none of these overlap with the flags below.
-  enum PrefRegistrationFlags {
+  enum PrefRegistrationFlags : uint32 {
     // No flags are specified.
     NO_REGISTRATION_FLAGS = 0,
 
     // The first 8 bits are reserved for subclasses of PrefRegistry to use.
+
+    // This marks the pref as "lossy". There is no strict time guarantee on when
+    // a lossy pref will be persisted to permanent storage when it is modified.
+    LOSSY_PREF = 1 << 8,
   };
 
   typedef PrefValueMap::const_iterator const_iterator;
   typedef base::hash_map<std::string, uint32> PrefRegistrationFlagsMap;
 
   PrefRegistry();
 
   // Retrieve the set of registration flags for the given preference. The return
   // value is a bitmask of PrefRegistrationFlags.
   uint32 GetRegistrationFlags(const std::string& pref_name) const;
@@ skipping 23 matching lines @@
   scoped_refptr<DefaultPrefStore> defaults_;
 
   // A map of pref name to a bitmask of PrefRegistrationFlags.
   PrefRegistrationFlagsMap registration_flags_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(PrefRegistry);
 };
 
 #endif  // BASE_PREFS_PREF_REGISTRY_H_