fix: detach webview instead of destroying it

Chromium no longer cleans up everything when a guest webcontents is
destroyed, we have to force detaching it and let Chromium destroy everything.

atom/browser/api/atom_api_web_contents_impl.cc

@@ -0,0 +1,52 @@
+// Copyright (c) 2018 GitHub, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#include "atom/browser/api/atom_api_web_contents.h"
+
+#include "content/browser/web_contents/web_contents_impl.h"
+
+#if BUILDFLAG(ENABLE_OSR)
+#include "atom/browser/osr/osr_render_widget_host_view.h"
+#include "atom/browser/osr/osr_web_contents_view.h"
+#endif
+
+// Including both web_contents_impl.h and node.h would introduce a error, we
+// have to isolate the usage of WebContentsImpl into a clean file to fix it:
+// error C2371: 'ssize_t': redefinition; different basic types
+
+namespace atom {
+
+namespace api {
+
+void WebContents::DetachFromOuterFrame() {
+  // See detach_webview_frame.patch on how to detach.
+  auto* impl = static_cast<content::WebContentsImpl*>(web_contents());
+  impl->GetRenderManagerForTesting()->RemoveOuterDelegateFrame();
+}
+
+#if BUILDFLAG(ENABLE_OSR)
+OffScreenWebContentsView* WebContents::GetOffScreenWebContentsView() const {
+  if (IsOffScreen()) {
+    const auto* impl =
+        static_cast<const content::WebContentsImpl*>(web_contents());
+    return static_cast<OffScreenWebContentsView*>(impl->GetView());
+  } else {
+    return nullptr;
+  }
+}
+
+OffScreenRenderWidgetHostView* WebContents::GetOffScreenRenderWidgetHostView()
+    const {
+  if (IsOffScreen()) {
+    return static_cast<OffScreenRenderWidgetHostView*>(
+        web_contents()->GetRenderWidgetHostView());
+  } else {
+    return nullptr;
+  }
+}
+#endif
+
+}  // namespace api
+
+}  // namespace atom