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

services/preferences/public/cpp/persistent_pref_store_client.cc

Index: services/preferences/public/cpp/persistent_pref_store_client.cc
diff --git a/services/preferences/public/cpp/persistent_pref_store_client.cc b/services/preferences/public/cpp/persistent_pref_store_client.cc
index 9bcb92fb1b6e3859e745c8360fc93dea0bcf42c5..0efd6a29014e4c3d70d0bfb93b11278a3a7482ec 100644
--- a/services/preferences/public/cpp/persistent_pref_store_client.cc
+++ b/services/preferences/public/cpp/persistent_pref_store_client.cc
@@ -146,7 +146,7 @@ void PersistentPrefStoreClient::OnConnect(
   error_delegate_.reset();
 
   if (connection->pref_store_connection) {
-    Init(std::move(connection->pref_store_connection->initial_prefs), true,
+    Init(&connection->pref_store_connection->initial_prefs, true,
          std::move(connection->pref_store_connection->observer));
   } else {
     Init(nullptr, false, nullptr);
@@ -170,11 +170,11 @@ void PersistentPrefStoreClient::FlushPendingWrites() {
   for (const auto& pref : pending_writes_) {
     const base::Value* value = nullptr;
     if (GetValue(pref.first, &value)) {
-      updates.push_back(mojom::PrefUpdate::New(
-          pref.first, value->CreateDeepCopy(), pref.second));
+      updates.push_back(
+          mojom::PrefUpdate::New(pref.first, *value, pref.second));
     } else {
       updates.push_back(
-          mojom::PrefUpdate::New(pref.first, nullptr, pref.second));
+          mojom::PrefUpdate::New(pref.first, base::nullopt, pref.second));
     }
   }
   pref_store_->SetValues(std::move(updates));