Fix TextInputClientMac related crashes of Fullscreen RenderWidget

content/browser/renderer_host/render_widget_host_delegate.cc

 // Copyright (c) 2012 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/renderer_host/render_widget_host_delegate.h"
 
 #include "build/build_config.h"
 #include "content/browser/renderer_host/render_view_host_delegate_view.h"
 #include "ui/gfx/geometry/rect.h"
 
@@ skipping 60 matching lines @@
 }
 
 bool RenderWidgetHostDelegate::IsHidden() {
   return false;
 }
 
 RenderViewHostDelegateView* RenderWidgetHostDelegate::GetDelegateView() {
   return nullptr;
 }
 
+RenderWidgetHostImpl* RenderWidgetHostDelegate::GetFullscreenRenderWidgetHost()
+    const {
+  return nullptr;
+}
+
 }  // namespace content