Dereference remote objects with native code

Previously we rely on the v8util.setDestructor to dereference the remote
objects in JavaScript, however as documented in V8, it is forbidden to
call V8 APIs in object's destructor (e.g. the weak callback), and doing
so would result in crashs.

This commit removes the JavaScript setDestructor method, and avoids
doing the dereference work with V8.

atom/common/api/remote_object_freer.cc

@@ -0,0 +1,63 @@
+// Copyright (c) 2016 GitHub, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#include "atom/common/api/remote_object_freer.h"
+
+#include "atom/common/api/api_messages.h"
+#include "base/strings/utf_string_conversions.h"
+#include "base/values.h"
+#include "content/public/renderer/render_view.h"
+#include "third_party/WebKit/public/web/WebLocalFrame.h"
+#include "third_party/WebKit/public/web/WebView.h"
+
+using blink::WebLocalFrame;
+using blink::WebView;
+
+namespace atom {
+
+namespace {
+
+content::RenderView* GetCurrentRenderView() {
+  WebLocalFrame* frame = WebLocalFrame::frameForCurrentContext();
+  if (!frame)
+    return nullptr;
+
+  WebView* view = frame->view();
+  if (!view)
+    return nullptr;  // can happen during closing.
+
+  return content::RenderView::FromWebView(view);
+}
+
+}  // namespace
+
+// static
+void RemoteObjectFreer::BindTo(
+    v8::Isolate* isolate, v8::Local<v8::Object> target, int object_id) {
+  new RemoteObjectFreer(isolate, target, object_id);
+}
+
+RemoteObjectFreer::RemoteObjectFreer(
+    v8::Isolate* isolate, v8::Local<v8::Object> target, int object_id)
+    : ObjectLifeMonitor(isolate, target),
+      object_id_(object_id) {
+}
+
+RemoteObjectFreer::~RemoteObjectFreer() {
+}
+
+void RemoteObjectFreer::RunDestructor() {
+  content::RenderView* render_view = GetCurrentRenderView();
+  if (!render_view)
+    return;
+
+  base::string16 channel = base::ASCIIToUTF16("ipc-message");
+  base::ListValue args;
+  args.AppendString("ELECTRON_BROWSER_DEREFERENCE");
+  args.AppendInteger(object_id_);
+  render_view->Send(
+      new AtomViewHostMsg_Message(render_view->GetRoutingID(), channel, args));
+}
+
+}  // namespace atom