Update from https://crrev.com/329939

base/prefs/pref_registry.h

Index: base/prefs/pref_registry.h
diff --git a/base/prefs/pref_registry.h b/base/prefs/pref_registry.h
index cc5804ef10a9d2e713be2dc9c50d205219f34c04..caf2a1afaf1daca90ba6242dd0456fc2efe94c86 100644
--- a/base/prefs/pref_registry.h
+++ b/base/prefs/pref_registry.h
@@ -32,11 +32,15 @@ class BASE_PREFS_EXPORT PrefRegistry : public base::RefCounted<PrefRegistry> {
   // 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;