Use timer task runner for V8PerIsolate tasks

gin/public/isolate_holder.h

Index: gin/public/isolate_holder.h
diff --git a/gin/public/isolate_holder.h b/gin/public/isolate_holder.h
index 7cf3d94ac898bed0ce2023d670fdb59082471e78..62b871085805716db97938f3dda6a44888cbfca6 100644
--- a/gin/public/isolate_holder.h
+++ b/gin/public/isolate_holder.h
@@ -8,10 +8,15 @@
 #include <memory>
 
 #include "base/macros.h"
+#include "base/memory/ref_counted.h"
 #include "gin/gin_export.h"
 #include "gin/public/v8_idle_task_runner.h"
 #include "v8/include/v8.h"
 
+namespace base {
+class SingleThreadTaskRunner;
+}
+
 namespace gin {
 
 class PerIsolateData;
@@ -42,8 +47,10 @@ class GIN_EXPORT IsolateHolder {
     kStableAndExperimentalV8Extras,
   };
 
-  IsolateHolder();
-  explicit IsolateHolder(AccessMode access_mode);
+  explicit IsolateHolder(
+      scoped_refptr<base::SingleThreadTaskRunner> task_runner);
+  IsolateHolder(scoped_refptr<base::SingleThreadTaskRunner> task_runner,
+                AccessMode access_mode);
   ~IsolateHolder();
 
   // Should be invoked once before creating IsolateHolder instances to