Pref service: add support for tracked prefs.

chrome/browser/profiles/profile_impl.h

Index: chrome/browser/profiles/profile_impl.h
diff --git a/chrome/browser/profiles/profile_impl.h b/chrome/browser/profiles/profile_impl.h
index 54093b9ce0309d2847af68e2365c746b9afa8582..7956e02e5246a6b9660071a8cb14e548e0ced412 100644
--- a/chrome/browser/profiles/profile_impl.h
+++ b/chrome/browser/profiles/profile_impl.h
@@ -50,12 +50,6 @@ class ProfilePolicyConnector;
 class SchemaRegistryService;
 }
 
-namespace prefs {
-namespace mojom {
-class TrackedPreferenceValidationDelegate;
-}
-}
-
 namespace ssl_config {
 class SSLConfigServiceManager;
 }
@@ -222,11 +216,6 @@ class ProfileImpl : public Profile {
       configuration_policy_provider_;
   std::unique_ptr<policy::ProfilePolicyConnector> profile_policy_connector_;
 
-  // Keep |pref_validation_delegate_| above |prefs_| so that the former outlives
-  // the latter.
-  std::unique_ptr<prefs::mojom::TrackedPreferenceValidationDelegate>
-      pref_validation_delegate_;
-
   // Keep |prefs_| on top for destruction order because |extension_prefs_|,
   // |io_data_| and others store pointers to |prefs_| and shall be destructed
   // first.