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

services/preferences/public/cpp/pref_store_impl.cc

Index: services/preferences/public/cpp/pref_store_impl.cc
diff --git a/services/preferences/public/cpp/pref_store_impl.cc b/services/preferences/public/cpp/pref_store_impl.cc
index c2289621e7e639db648661299ff750a2a5d96d83..a497a898c71259beb5a1e2e0469d5cccf53b76db 100644
--- a/services/preferences/public/cpp/pref_store_impl.cc
+++ b/services/preferences/public/cpp/pref_store_impl.cc
@@ -27,7 +27,7 @@ class PrefStoreImpl::Observer {
       return;
 
     std::vector<mojom::PrefUpdatePtr> updates;
-    updates.push_back(mojom::PrefUpdate::New(key, value.CreateDeepCopy(), 0));
+    updates.push_back(mojom::PrefUpdate::New(key, value, 0));
     observer_->OnPrefsChanged(std::move(updates));
   }
 
@@ -36,7 +36,7 @@ class PrefStoreImpl::Observer {
       return;
 
     std::vector<mojom::PrefUpdatePtr> updates;
-    updates.push_back(mojom::PrefUpdate::New(key, nullptr, 0));
+    updates.push_back(mojom::PrefUpdate::New(key, base::nullopt, 0));
     observer_->OnPrefsChanged(std::move(updates));
   }
 
@@ -106,7 +106,7 @@ void PrefStoreImpl::AddObserver(
       std::unordered_set<std::string>(prefs_to_observe.begin(),
                                       prefs_to_observe.end())));
   callback.Run(mojom::PrefStoreConnection::New(
-      std::move(request), backing_pref_store_->GetValues(),
+      std::move(request), *backing_pref_store_->GetValues(),
       backing_pref_store_->IsInitializationComplete()));
 }