Use explicit WebString conversions in plugins code

chrome/renderer/plugins/chrome_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 "chrome/renderer/plugins/chrome_plugin_placeholder.h"
 
 #include <memory>
 #include <utility>
 
 #include "base/command_line.h"
@@ skipping 86 matching lines @@
           IDR_BLOCKED_PLUGIN_HTML));
 
   base::DictionaryValue values;
   values.SetString("message",
                    l10n_util::GetStringUTF8(IDS_PLUGIN_NOT_SUPPORTED));
 
   std::string html_data = webui::GetI18nTemplateHtml(template_html, &values);
 
   // Will destroy itself when its WebViewPlugin is going away.
   return new ChromePluginPlaceholder(render_frame, frame, params, html_data,
-                                     params.mimeType);
+                                     params.mimeType.utf16());
 }
 
 // static
 ChromePluginPlaceholder* ChromePluginPlaceholder::CreateBlockedPlugin(
     content::RenderFrame* render_frame,
     blink::WebLocalFrame* frame,
     const blink::WebPluginParams& params,
     const content::WebPluginInfo& info,
     const std::string& identifier,
     const base::string16& name,
@@ skipping 295 matching lines @@
 
   if (base::CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kEnablePluginPlaceholderTesting)) {
     builder.SetMethod<void (ChromePluginPlaceholder::*)()>(
         "didFinishIconRepositionForTesting",
         &ChromePluginPlaceholder::DidFinishIconRepositionForTestingCallback);
   }
 
   return builder;
 }