Convert TrackedPreferenceValidationDelegate into a mojo interface.

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 f4945cc88777b7b61a7f01da8998330c2aafa68a..eaf5225bfe569dc020b4dedc8e48f6ea8e0cea85 100644
--- a/chrome/browser/profiles/profile_impl.h
+++ b/chrome/browser/profiles/profile_impl.h
@@ -27,8 +27,6 @@
 
 class PrefService;
 
-class TrackedPreferenceValidationDelegate;
-
 #if defined(OS_CHROMEOS)
 namespace chromeos {
 class KioskTest;
@@ -52,6 +50,12 @@ class ProfilePolicyConnector;
 class SchemaRegistryService;
 }
 
+namespace prefs {
+namespace mojom {
+class TrackedPreferenceValidationDelegate;
+}
+}
+
 namespace ssl_config {
 class SSLConfigServiceManager;
 }
@@ -215,7 +219,7 @@ class ProfileImpl : public Profile {
 
   // Keep |pref_validation_delegate_| above |prefs_| so that the former outlives
   // the latter.
-  std::unique_ptr<TrackedPreferenceValidationDelegate>
+  std::unique_ptr<prefs::mojom::TrackedPreferenceValidationDelegate>
       pref_validation_delegate_;
 
   // Keep |prefs_| on top for destruction order because |extension_prefs_|,