Make <webview> use out-of-process iframe architecture.

extensions/renderer/guest_view/extensions_guest_view_container.h

Index: extensions/renderer/guest_view/extensions_guest_view_container.h
diff --git a/extensions/renderer/guest_view/extensions_guest_view_container.h b/extensions/renderer/guest_view/extensions_guest_view_container.h
index aabb47e68f07f8c4bf8a31f1ce9edca7ee67ec9e..35f2211568cee47b4bc1eb350b6ce2dc7563c830 100644
--- a/extensions/renderer/guest_view/extensions_guest_view_container.h
+++ b/extensions/renderer/guest_view/extensions_guest_view_container.h
@@ -20,8 +20,6 @@ class ExtensionsGuestViewContainer : public guest_view::GuestViewContainer {
  public:
   explicit ExtensionsGuestViewContainer(content::RenderFrame* render_frame);
 
-  void RegisterDestructionCallback(v8::Local<v8::Function> callback,
-                                   v8::Isolate* isolate);
   void RegisterElementResizeCallback(v8::Local<v8::Function> callback,
                                      v8::Isolate* isolate);
 
@@ -37,9 +35,6 @@ class ExtensionsGuestViewContainer : public guest_view::GuestViewContainer {
   // GuestViewContainer implementation.
   void OnDestroy(bool embedder_frame_destroyed) override;
 
-  v8::Global<v8::Function> destruction_callback_;
-  v8::Isolate* destruction_isolate_;
-
   v8::Global<v8::Function> element_resize_callback_;
   v8::Isolate* element_resize_isolate_;