Reduce usage of MessageLoopProxy in base/

base/memory/ref_counted_delete_on_task_runner.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 BASE_MEMORY_REF_COUNTED_DELETE_ON_TASK_RUNNER_H_
+#define BASE_MEMORY_REF_COUNTED_DELETE_ON_TASK_RUNNER_H_
+
+#include "base/location.h"
+#include "base/logging.h"
+#include "base/memory/ref_counted.h"
+#include "base/sequenced_task_runner.h"
+
+namespace base {
+
+// RefCountedDeleteOnTaskRunner is similar to RefCountedThreadSafe, and ensures
+// that the object will be deleted on a specified task runner.
+//
+// Sample usage:
+// class Foo : public RefCountedDeleteOnTaskRunner<Foo> {
+//
+//   Foo(const scoped_refptr<SequencedTaskRunner>& task_runner)
+//       : RefCountedDeleteOnTaskRunner<Foo>(task_runner) {
+//     ...
+//   }
+//   ...
+//  private:
+//   friend class RefCountedDeleteOnTaskRunner<Foo>;
+//   friend class DeleteHelper<Foo>;
+//
+//   ~Foo();
+// };
+
+template <class T>
+class RefCountedDeleteOnTaskRunner : public subtle::RefCountedThreadSafeBase {
+ public:
+  explicit RefCountedDeleteOnTaskRunner(
+      const scoped_refptr<SequencedTaskRunner>& task_runner)
+      : task_runner_(task_runner) {
+    DCHECK(task_runner_.get());
+  }
+
+  void AddRef() const { subtle::RefCountedThreadSafeBase::AddRef(); }
+
+  void Release() const {
+    if (subtle::RefCountedThreadSafeBase::Release())
+      DestructOnTaskRunner();
+  }
+
+ protected:
+  friend class DeleteHelper<RefCountedDeleteOnTaskRunner>;
+  ~RefCountedDeleteOnTaskRunner() {}
+
+  void DestructOnTaskRunner() const {
+    const T* t = static_cast<const T*>(this);
+    if (task_runner_->RunsTasksOnCurrentThread())
+      delete t;
+    else
+      task_runner_->DeleteSoon(FROM_HERE, t);
+  }
+
+  scoped_refptr<SequencedTaskRunner> task_runner_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(RefCountedDeleteOnTaskRunner);
+};
+
+}  // namespace base
+
+#endif  // BASE_MEMORY_REF_COUNTED_DELETE_ON_TASK_RUNNER_H_