Clear input event router entries for destroyed RWHVGuests

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 540 matching lines @@
     gfx::NativeViewAccessible accessible_parent) {
 }
 
 gfx::NativeViewId RenderWidgetHostViewGuest::GetParentForWindowlessPlugin()
     const {
   return NULL;
 }
 #endif
 
 void RenderWidgetHostViewGuest::DestroyGuestView() {
+  UnregisterSurfaceNamespaceId();

[wjmaclean, 2016/01/27 21:39:28]

So this eventually calls back to  WebContentsImpl::GetInputEventRouter() which
will give one of two answers, depending on whether the Guest WebContents has
been 'detached' from the owner WebContents (GetOuterWebContents()).

Since this also gets called from BrowserPluginGuest::OnDetach() we can hope that
GetOuterWebContents() is still non-null in the crash case, ** so this is worth
trying **. But if the crashes continue to occur, we should next try to check to
see if the owner has gone away unexpectedly somehow ...

   host_->SetView(NULL);
   host_ = NULL;
   base::MessageLoop::current()->DeleteSoon(FROM_HERE, this);
 }
 
 bool RenderWidgetHostViewGuest::ForwardGestureEventToRenderer(
     ui::GestureEvent* gesture) {
 #if defined(USE_AURA)
   if (!host_)
     return false;
@@ skipping 132 matching lines @@
     if (gesture_event.type == blink::WebInputEvent::GestureScrollUpdate &&
         gesture_event.data.scrollUpdate.inertial) {
       return;
     }
     host_->ForwardGestureEvent(gesture_event);
     return;
   }
 }
 
 }  // namespace content