RenderWidgetHostViewChildFrame's called a virtual in its ctor.

content/browser/frame_host/render_widget_host_view_guest.cc

 // 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.
 
 #include "content/browser/frame_host/render_widget_host_view_guest.h"
 
 #include <utility>
 
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
@@ skipping 58 matching lines @@
     RenderWidgetHost* widget_host,
     BrowserPluginGuest* guest,
     base::WeakPtr<RenderWidgetHostViewBase> platform_view)
     : RenderWidgetHostViewChildFrame(widget_host),
       // |guest| is NULL during test.
       guest_(guest ? guest->AsWeakPtr() : base::WeakPtr<BrowserPluginGuest>()),
       platform_view_(platform_view) {
   gfx::NativeView view = GetNativeView();
   if (view)
     UpdateScreenInfo(view);
+  Init();

[clamy, 2016/10/05 12:35:53]

nit: For the sake of consistency, I think it'd be nicer to have a create
function that mirrors what is done in RenderWidgetHostViewChildFrame.

[dtapuska, 2016/10/05 14:25:00]

Done.

 }
 
 RenderWidgetHostViewGuest::~RenderWidgetHostViewGuest() {}
 
 bool RenderWidgetHostViewGuest::OnMessageReceivedFromEmbedder(
     const IPC::Message& message,
     RenderWidgetHostImpl* embedder) {
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP_WITH_PARAM(RenderWidgetHostViewGuest, message,
                                    embedder)
@@ skipping 588 matching lines @@
         gesture_event.data.scrollUpdate.inertialPhase ==
             blink::WebGestureEvent::MomentumPhase) {
       return;
     }
     host_->ForwardGestureEvent(gesture_event);
     return;
   }
 }
 
 }  // namespace content