Introduce extras export object.

test/cctest/test-api.cc

Index: test/cctest/test-api.cc
diff --git a/test/cctest/test-api.cc b/test/cctest/test-api.cc
index 9e9e03a937910963966f923e4bad19aa7d30c2ce..a63ad9390ef58b0aad88ce081a87c0d85ebcc69f 100644
--- a/test/cctest/test-api.cc
+++ b/test/cctest/test-api.cc
@@ -21101,3 +21101,21 @@ TEST(StrongModeArityCallFromApi2) {
     CHECK(!try_catch.HasCaught());
   }
 }
+
+
+TEST(ExtrasExportsObject) {
+  v8::Isolate* isolate = CcTest::isolate();
+  v8::HandleScope handle_scope(isolate);
+  LocalContext env;
+
+  // standalone.gypi ensures we include the test-extra.js file, which should
+  // add the testExtraShouldReturnFive export
+  v8::Local<v8::Object> exports = env->GetExtrasExportsObject();
+
+  auto func =
+      exports->Get(v8_str("testExtraShouldReturnFive")).As<v8::Function>();
+  auto undefined = v8::Undefined(isolate);
+  auto result = func->Call(undefined, 0, {}).As<v8::Number>();
+
+  CHECK(result->Value() == 5.0);
+}