Switch base::Value typemapping to be by value instead of by unique_ptr.

services/preferences/tracked/tracked_atomic_preference.cc

Index: services/preferences/tracked/tracked_atomic_preference.cc
diff --git a/services/preferences/tracked/tracked_atomic_preference.cc b/services/preferences/tracked/tracked_atomic_preference.cc
index 8df3a3609fa096f6651669c88a17f668111c8dd0..48e05ac702bb0c93c76862be89e8d1ca424c9555 100644
--- a/services/preferences/tracked/tracked_atomic_preference.cc
+++ b/services/preferences/tracked/tracked_atomic_preference.cc
@@ -56,8 +56,8 @@ bool TrackedAtomicPreference::EnforceAndReport(
 
   if (delegate_) {
     delegate_->OnAtomicPreferenceValidation(
-        pref_path_, value ? value->CreateDeepCopy() : nullptr, value_state,
-        external_validation_value_state, helper_.IsPersonal());
+        pref_path_, value ? base::Optional<base::Value>(*value) : base::nullopt,
+        value_state, external_validation_value_state, helper_.IsPersonal());
   }
   TrackedPreferenceHelper::ResetAction reset_action =
       helper_.GetAction(value_state);