Tolerate a null WebScheduler in utility process V8 initialization

gin/per_isolate_data.cc

Index: gin/per_isolate_data.cc
diff --git a/gin/per_isolate_data.cc b/gin/per_isolate_data.cc
index dd4ce9daab94f29b1aadacb5c697c06007d7bd55..029b93d5f7a1724ab36fb66c8db5b782d794942c 100644
--- a/gin/per_isolate_data.cc
+++ b/gin/per_isolate_data.cc
@@ -29,7 +29,8 @@ PerIsolateData::PerIsolateData(
     : isolate_(isolate),
       allocator_(allocator),
       access_mode_(access_mode),
-      task_runner_(task_runner) {
+      task_runner_(
+          task_runner ? task_runner : base::ThreadTaskRunnerHandle::Get()) {
   isolate_->SetData(kEmbedderNativeGin, this);
 }