Use PostTaskAndReplyWithResult in plugin_service_impl.cc.

content/test/fake_plugin_service.h

 // 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.
 
 #ifndef CONTENT_TEST_FAKE_PLUGIN_SERVICE_H_
 #define CONTENT_TEST_FAKE_PLUGIN_SERVICE_H_
 
 #include "base/macros.h"
 #include "build/build_config.h"
 #include "content/public/browser/plugin_service.h"
@@ skipping 22 matching lines @@
                      const url::Origin& main_frame_origin,
                      const std::string& mime_type,
                      bool allow_wildcard,
                      bool* is_stale,
                      WebPluginInfo* info,
                      std::string* actual_mime_type) override;
   bool GetPluginInfoByPath(const base::FilePath& plugin_path,
                            WebPluginInfo* info) override;
   base::string16 GetPluginDisplayNameByPath(
       const base::FilePath& path) override;
-  void GetPlugins(const GetPluginsCallback& callback) override;
+  void GetPlugins(GetPluginsCallback callback) override;
   PepperPluginInfo* GetRegisteredPpapiPluginInfo(
       const base::FilePath& plugin_path) override;
   void SetFilter(PluginServiceFilter* filter) override;
   PluginServiceFilter* GetFilter() override;
   bool IsPluginUnstable(const base::FilePath& plugin_path) override;
   void RefreshPlugins() override;
   void RegisterInternalPlugin(const WebPluginInfo& info,
                               bool add_at_beginning) override;
   void UnregisterInternalPlugin(const base::FilePath& path) override;
   void GetInternalPlugins(std::vector<WebPluginInfo>* plugins) override;
   bool PpapiDevChannelSupported(BrowserContext* browser_context,
                                 const GURL& document_url) override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FakePluginService);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_TEST_FAKE_PLUGIN_SERVICE_H_