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

services/preferences/tracked/tracked_atomic_preference.cc

 // Copyright 2014 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.
 
 #include "services/preferences/tracked/tracked_atomic_preference.h"
 
 #include "base/values.h"
 #include "services/preferences/public/interfaces/tracked_preference_validation_delegate.mojom.h"
 #include "services/preferences/tracked/pref_hash_store_transaction.h"
 
@@ skipping 38 matching lines @@
   if (external_validation_transaction) {
     external_validation_value_state =
         external_validation_transaction->CheckValue(pref_path_, value);
     helper_.ReportValidationResult(
         external_validation_value_state,
         external_validation_transaction->GetStoreUMASuffix());
   }
 
   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);
   helper_.ReportAction(reset_action);
 
   bool was_reset = false;
   if (reset_action == TrackedPreferenceHelper::DO_RESET) {
     pref_store_contents->RemovePath(pref_path_, NULL);
     was_reset = true;
   }
 
   if (value_state != ValueState::UNCHANGED) {
     // Store the hash for the new value (whether it was reset or not).
     const base::Value* new_value = NULL;
     pref_store_contents->Get(pref_path_, &new_value);
     transaction->StoreHash(pref_path_, new_value);
   }
 
   // Update MACs in the external store if there is one and there either was a
   // reset or external validation failed.
   if (external_validation_transaction &&
       (was_reset || external_validation_value_state != ValueState::UNCHANGED)) {
     const base::Value* new_value = nullptr;
     pref_store_contents->Get(pref_path_, &new_value);
     external_validation_transaction->StoreHash(pref_path_, new_value);
   }
 
   return was_reset;
 }