Update from https://crrev.com/327068

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"
 #include "base/prefs/pref_value_map.h"
 
 namespace base {
 class Value;
 }
 
 class DefaultPrefStore;
 class PrefStore;
 
 // Preferences need to be registered with a type and default value
 // before they are used.
 //
 // The way you use a PrefRegistry is that you register all required
 // preferences on it (via one of its subclasses), then pass it as a
 // 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 {
+    // No flags are specified.
+    NO_REGISTRATION_FLAGS = 0,
+
+    // The first 8 bits are reserved for subclasses of PrefRegistry to use.
+  };
+
   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;
+
   // Gets the registered defaults.
   scoped_refptr<PrefStore> defaults();
 
   // Allows iteration over defaults.
   const_iterator begin() const;
   const_iterator end() const;
 
   // Changes the default value for a preference. Takes ownership of |value|.
   //
   // |pref_name| must be a previously registered preference.
   void SetDefaultPrefValue(const std::string& pref_name, base::Value* value);
 
  protected:
   friend class base::RefCounted<PrefRegistry>;
   virtual ~PrefRegistry();
 
-  // Used by subclasses to register a default value for a preference.
-  void RegisterPreference(const std::string& path, base::Value* default_value);
+  // Used by subclasses to register a default value and registration flags for
+  // a preference. |flags| is a bitmask of |PrefRegistrationFlags|.
+  void RegisterPreference(const std::string& path,
+                          base::Value* default_value,
+                          uint32 flags);
 
   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_