Enable shadow DOM-based "missing plugin" placeholder.

content/public/renderer/content_renderer_client.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/public/renderer/content_renderer_client.h"
 
 namespace content {
 
 SkBitmap* ContentRendererClient::GetSadPluginBitmap() {
   return NULL;
 }
 
 SkBitmap* ContentRendererClient::GetSadWebViewBitmap() {
   return NULL;
 }
 
+blink::WebPluginPlaceholder*
+ContentRendererClient::OverrideCreatePluginPlaceholder(
+    RenderFrame* render_frame,
+    blink::WebLocalFrame* frame,
+    const blink::WebPluginParams& params) {
+  return nullptr;
+}
+
 bool ContentRendererClient::OverrideCreatePlugin(
     RenderFrame* render_frame,
     blink::WebLocalFrame* frame,
     const blink::WebPluginParams& params,
     blink::WebPlugin** plugin) {
   return false;
 }
 
 blink::WebPlugin* ContentRendererClient::CreatePluginReplacement(
     RenderFrame* render_frame,
@@ skipping 163 matching lines @@
     RenderFrame* render_frame,
     const std::string& mime_type) {
   return NULL;
 }
 
 std::string ContentRendererClient::GetUserAgentOverrideForURL(const GURL& url) {
   return std::string();
 }
 
 }  // namespace content