Use timer task runner for V8PerIsolate tasks

gin/shell_runner_unittest.cc

Index: gin/shell_runner_unittest.cc
diff --git a/gin/shell_runner_unittest.cc b/gin/shell_runner_unittest.cc
index abd4f3cb755b3fe3b13bcc84fec4e8c58cbd9006..0743ededb62ed7f9bb77b202cf6765da314a62a7 100644
--- a/gin/shell_runner_unittest.cc
+++ b/gin/shell_runner_unittest.cc
@@ -6,6 +6,7 @@
 
 #include "base/compiler_specific.h"
 #include "base/message_loop/message_loop.h"
+#include "base/threading/thread_task_runner_handle.h"
 #include "gin/array_buffer.h"
 #include "gin/converter.h"
 #include "gin/public/isolate_holder.h"
@@ -35,7 +36,7 @@ TEST(RunnerTest, Run) {
   gin::IsolateHolder::Initialize(gin::IsolateHolder::kStrictMode,
                                  gin::IsolateHolder::kStableV8Extras,
                                  gin::ArrayBufferAllocator::SharedInstance());
-  gin::IsolateHolder instance;
+  gin::IsolateHolder instance(base::ThreadTaskRunnerHandle::Get());
 
   ShellRunnerDelegate delegate;
   Isolate* isolate = instance.isolate();