Add plugins::TestPluginPlaceholder class and allow its use in Blink layout tests.

components/plugins/renderer/plugin_placeholder.cc

 // Copyright 2013 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 "components/plugins/renderer/plugin_placeholder.h"
 
+#include "content/public/common/web_preferences.h"
 #include "content/public/renderer/render_frame.h"
 
 namespace plugins {
 
 gin::WrapperInfo PluginPlaceholder::kWrapperInfo = {gin::kEmbedderNativeGin};
 
 PluginPlaceholder::PluginPlaceholder(content::RenderFrame* render_frame,
                                      blink::WebLocalFrame* frame,
                                      const blink::WebPluginParams& params,
                                      const std::string& html_data,
                                      GURL placeholderDataUrl)
     : content::RenderFrameObserver(render_frame),
       frame_(frame),
       plugin_params_(params),
       plugin_(WebViewPlugin::Create(this,
-                                    render_frame->GetWebkitPreferences(),
+                                    render_frame
+                                        ? render_frame->GetWebkitPreferences()
+                                        : content::WebPreferences(),
                                     html_data,
                                     placeholderDataUrl)) {
   DCHECK(placeholderDataUrl.is_valid())
       << "Blink requires the placeholder to have a valid URL.";
 }
 
 PluginPlaceholder::~PluginPlaceholder() {}
 
 const blink::WebPluginParams& PluginPlaceholder::GetPluginParams() const {
   return plugin_params_;
@@ skipping 14 matching lines @@
   return v8::Local<v8::Object>();
 }
 
 void PluginPlaceholder::OnDestruct() {
   frame_ = NULL;
 }
 
 blink::WebLocalFrame* PluginPlaceholder::GetFrame() { return frame_; }
 
 }  // namespace plugins