Add a declarative way in c/b/s/sync_prefs.cc to say which data types have prefs

chrome/browser/sync/sync_prefs.h

 // Copyright (c) 2011 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 CHROME_BROWSER_SYNC_SYNC_PREFS_H_
 #define CHROME_BROWSER_SYNC_SYNC_PREFS_H_
 #pragma once
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
@@ skipping 100 matching lines @@
   virtual void Observe(int type,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
   // For testing.
 
   void SetManagedForTest(bool is_managed);
   syncable::ModelTypeSet GetAcknowledgeSyncedTypesForTest() const;
 
  private:
+  void RegisterDeterminedTypes();
   void RegisterPreferences();
 
   void RegisterDataTypePreferredPref(
       syncable::ModelType type, bool is_preferred);
   bool GetDataTypePreferred(syncable::ModelType type) const;
   void SetDataTypePreferred(syncable::ModelType type, bool is_preferred);
 
   base::NonThreadSafe non_thread_safe_;
 
   // May be NULL.
   PrefService* const pref_service_;
 
   ObserverList<SyncPrefObserver> sync_pref_observers_;
 
   // The preference that controls whether sync is under control by
   // configuration management.
   BooleanPrefMember pref_sync_managed_;
 
+  // Data types where the enable/disabled preference is determined by another
+  // type, such APP_NOTIFICATIONS being determined by APPS. This is map from
+  // determined type (APP_NOTIFICATIONS) -> determining type (APPS).
+  typedef std::map<syncable::ModelType, syncable::ModelType>
+      TypesDeterminedByMap;

[akalin, 2012/02/29 05:33:03]

These names are kinda awkward.  How about:

typedef ... TypeDependencyMap;
TypeDependencyMap type_dependencies_;

[not at google - send to devlin, 2012/03/01 03:14:40]

I avoided using the term "dependency" because it gives the wrong connotation in
the context of software; I think of "A is a dependency of B" as meaning that "A
must be in a valid state before we can think about B", but that's not what this
is. Maybe "DependentTypesMap"/"dependent_types_" would be more accurate?

Or maybe this is thinking about the wrong way. Chatting to a colleague, perhaps
a more sensible model would be to think of it as "pref groups" such that the
value of one pref determines the values of a group of prefs. So this would be

// Groups of prefs that always have the same value as a master pref.
// For example, the APPS group has {APP_NOTIFICATIONS, APP_SETTINGS}
// (as well as APPS, but that is implied), so
//   pref_groups_[syncable::APPS] = { syncable::APP_NOTIFICATIONS,
syncable::APP_SETTINGS}
//   pref_groups_[syncable::EXTENSIONS = { syncable::EXTENSION_SETTINGS }
// etc.
typedef std::map<syncable::ModelType, ModelTypeSet> PrefGroupsMap;
PrefGroupsMap pref_groups_;

It'd also be slightly more efficient that way.

In the meantime though, pending your opinion about this, I'll go with the
original plan and use DependentTypesMap/dependent_types_.

+  TypesDeterminedByMap types_determined_by_;
+
   DISALLOW_COPY_AND_ASSIGN(SyncPrefs);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_SYNC_PREFS_H_