sync: Implementation of Priority Preferences.

components/user_prefs/pref_registry_syncable.h

Index: components/user_prefs/pref_registry_syncable.h
diff --git a/components/user_prefs/pref_registry_syncable.h b/components/user_prefs/pref_registry_syncable.h
index 08477f249fe30a117f8d281a1d462ee329b11e94..811209ba722f28142c5462b82efab54fa3f85369 100644
--- a/components/user_prefs/pref_registry_syncable.h
+++ b/components/user_prefs/pref_registry_syncable.h
@@ -30,19 +30,27 @@ class Value;
 // does this for Chrome.
 class USER_PREFS_EXPORT PrefRegistrySyncable : public PrefRegistry {
  public:
-  typedef base::Callback<void(const char* path)> SyncableRegistrationCallback;
-
   // Enum used when registering preferences to determine if it should
-  // be synced or not.
+  // be synced or not. Syncable priority preferences are preferences that are
+  // never encrypted and are synced before other datatypes. Because they're
+  // never encrypted, on first sync, they can be synced down before the user
+  // is prompted for a passphrase.
   enum PrefSyncStatus {
     UNSYNCABLE_PREF,
-    SYNCABLE_PREF
+    SYNCABLE_PREF,
+    SYNCABLE_PRIORITY_PREF,
   };
 
+  typedef
+      base::Callback<void(const char* path, const PrefSyncStatus sync_status)>
+          SyncableRegistrationCallback;
+
   PrefRegistrySyncable();
 
+  typedef std::map<std::string, PrefSyncStatus> PrefToStatus;
+
   // Retrieve the set of syncable preferences currently registered.
-  const std::set<std::string>& syncable_preferences() const;
+  const PrefToStatus& syncable_preferences() const;
 
   // Exactly one callback can be set for the event of a syncable
   // preference being registered. It will be fired after the
@@ -111,7 +119,7 @@ class USER_PREFS_EXPORT PrefRegistrySyncable : public PrefRegistry {
   SyncableRegistrationCallback callback_;
 
   // Contains the names of all registered preferences that are syncable.
-  std::set<std::string> syncable_preferences_;
+  PrefToStatus syncable_preferences_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefRegistrySyncable);
 };