Set V8 extras mode in gin::V8Initializer.

third_party/mojo/src/mojo/edk/js/tests/js_to_cpp_tests.cc

Index: third_party/mojo/src/mojo/edk/js/tests/js_to_cpp_tests.cc
diff --git a/third_party/mojo/src/mojo/edk/js/tests/js_to_cpp_tests.cc b/third_party/mojo/src/mojo/edk/js/tests/js_to_cpp_tests.cc
index e265e6ace70292fb70ba3285a94993d25c273d3b..a1da8096336bb4c48f28f7f657935fe002ad9863 100644
--- a/third_party/mojo/src/mojo/edk/js/tests/js_to_cpp_tests.cc
+++ b/third_party/mojo/src/mojo/edk/js/tests/js_to_cpp_tests.cc
@@ -381,6 +381,7 @@ class JsToCppTest : public testing::Test {
     js_side->SetCppSide(cpp_side_ptr.Pass());
 
     gin::IsolateHolder::Initialize(gin::IsolateHolder::kStrictMode,
+                                   gin::IsolateHolder::kStableV8Extras,
                                    gin::ArrayBufferAllocator::SharedInstance());
     gin::IsolateHolder instance;
     MojoRunnerDelegate delegate;