Replace the gc extension in content shell with a gin::Wrappable class

content/shell/renderer/gc_extension.h

Index: content/shell/renderer/gc_extension.h
diff --git a/content/shell/renderer/gc_extension.h b/content/shell/renderer/gc_extension.h
deleted file mode 100644
index 4970a1c37095a33f7866a34deb2856e13cc28582..0000000000000000000000000000000000000000
--- a/content/shell/renderer/gc_extension.h
+++ /dev/null
@@ -1,23 +0,0 @@
-// 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 CONTENT_SHELL_RENDERER_GC_EXTENSION_H_
-#define CONTENT_SHELL_RENDERER_GC_EXTENSION_H_
-
-namespace v8 {
-class Extension;
-}
-
-namespace extensions_v8 {
-
-// GCExtension is a v8 extension to expose a method into JS for triggering
-// garbage collection. This should only be used for debugging.
-class GCExtension {
- public:
-  static v8::Extension* Get();
-};
-
-}  // namespace extensions_v8
-
-#endif  // CONTENT_SHELL_RENDERER_GC_EXTENSION_H_