Introduce per-tab preferences service.

chrome/browser/prefs/pref_model_associator.h

Index: chrome/browser/prefs/pref_model_associator.h
diff --git a/chrome/browser/prefs/pref_model_associator.h b/chrome/browser/prefs/pref_model_associator.h
index 5e2189cfc375486907207b86f9cb3d8ccb15b722..8cb22d69858b1502a5a3500ea7f99a335bed378e 100644
--- a/chrome/browser/prefs/pref_model_associator.h
+++ b/chrome/browser/prefs/pref_model_associator.h
@@ -32,7 +32,7 @@ class PrefModelAssociator
     : public SyncableService,
       public base::NonThreadSafe {
  public:
-  explicit PrefModelAssociator(PrefService* pref_service);
+  PrefModelAssociator();
   virtual ~PrefModelAssociator();
 
   // SyncableService implementation.
@@ -85,13 +85,11 @@ class PrefModelAssociator
       std::string* name);
 
  protected:
+  friend class PrefService;
   friend class ProfileSyncServicePreferenceTest;
 
   typedef std::map<std::string, SyncData> SyncDataMap;
 
-  // For testing.
-  PrefModelAssociator();
-
   // Create an association for a given preference. If |sync_pref| is valid,
   // signifying that sync has data for this preference, we reconcile their data
   // with ours and append a new UPDATE SyncChange to |sync_changes|. If
@@ -104,6 +102,8 @@ class PrefModelAssociator
                             const std::string& pref_name,
                             SyncChangeList* sync_changes);
 
+  void SetPrefService(PrefService* pref_service);
+
   static base::Value* MergeListValues(
       const base::Value& from_value, const base::Value& to_value);
   static base::Value* MergeDictionaryValues(const base::Value& from_value,