Use timer task runner for V8PerIsolate tasks

gin/public/isolate_holder.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef GIN_PUBLIC_ISOLATE_HOLDER_H_
 #define GIN_PUBLIC_ISOLATE_HOLDER_H_
 
 #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;
 class RunMicrotasksObserver;
 class V8IsolateMemoryDumpProvider;
 
 // To embed Gin, first initialize gin using IsolateHolder::Initialize and then
 // create an instance of IsolateHolder to hold the v8::Isolate in which you
 // will execute JavaScript. You might wish to subclass IsolateHolder if you
 // want to tie more state to the lifetime of the isolate.
@@ skipping 10 matching lines @@
     kSingleThread,
     kUseLocker
   };
 
   // Indicates whether V8 works with stable or experimental v8 extras.
   enum V8ExtrasMode {
     kStableV8Extras,
     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
   // initialize V8 and Gin. In case V8_USE_EXTERNAL_STARTUP_DATA is
   // defined, V8's initial natives should be loaded (by calling
   // V8Initializer::LoadV8NativesFromFD or
   // V8Initializer::LoadV8Natives) before calling this method.  If the
   // snapshot file is available, it should also be loaded (by calling
   // V8Initializer::LoadV8SnapshotFromFD or
   // V8Initializer::LoadV8Snapshot) before calling this method.
@@ skipping 33 matching lines @@
   std::unique_ptr<RunMicrotasksObserver> task_observer_;
   std::unique_ptr<V8IsolateMemoryDumpProvider> isolate_memory_dump_provider_;
   AccessMode access_mode_;
 
   DISALLOW_COPY_AND_ASSIGN(IsolateHolder);
 };
 
 }  // namespace gin
 
 #endif  // GIN_PUBLIC_ISOLATE_HOLDER_H_