Remove unused class UnsafePersistent.

extensions/renderer/unsafe_persistent.h

-// Copyright 2014 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 EXTENSIONS_RENDERER_UNSAFE_PERSISTENT_H_
-#define EXTENSIONS_RENDERER_UNSAFE_PERSISTENT_H_
-
-#include "v8/include/v8.h"
-
-namespace extensions {
-
-// An unsafe way to pass Persistent handles around. Do not use unless you know
-// what you're doing. UnsafePersistent is only safe to use when we know that the
-// memory pointed by it is not going away: 1) When GC cannot happen while the
-// UnsafePersistent is alive or 2) when there is a strong Persistent keeping the
-// memory alive while the UnsafePersistent is alive.
-template <typename T>
-class UnsafePersistent {
- public:
-  UnsafePersistent() : value_(0) {}
-
-  explicit UnsafePersistent(v8::Persistent<T>* handle) {
-    value_ = handle->ClearAndLeak();
-  }
-
-  UnsafePersistent(v8::Isolate* isolate, const v8::Handle<T>& handle) {
-    v8::Persistent<T> persistent(isolate, handle);
-    value_ = persistent.ClearAndLeak();
-  }
-
-  // Usage of this function requires
-  // V8_ALLOW_ACCESS_TO_RAW_HANDLE_CONSTRUCTOR to be defined
-  void dispose() {
-    v8::Persistent<T> handle(value_);
-    handle.Reset();
-    value_ = 0;
-  }
-
-  // Usage of this function requires
-  // V8_ALLOW_ACCESS_TO_RAW_HANDLE_CONSTRUCTOR to be defined
-  v8::Local<T> newLocal(v8::Isolate* isolate) {
-    return v8::Local<T>::New(isolate, v8::Local<T>(value_));
-  }
-
- private:
-  T* value_;
-};
-
-}  // namespace extensions
-
-#endif  // EXTENSIONS_RENDERER_UNSAFE_PERSISTENT_H_