Remove RuntimeAPIDelegate::GetPreviousVersion.

extensions/shell/browser/shell_runtime_api_delegate.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 EXTENSIONS_SHELL_BROWSER_SHELL_RUNTIME_API_DELEGATE_H_
 #define EXTENSIONS_SHELL_BROWSER_SHELL_RUNTIME_API_DELEGATE_H_
 
 #include "base/macros.h"
 #include "extensions/browser/api/runtime/runtime_api_delegate.h"
 
 namespace extensions {
 
 class ShellRuntimeAPIDelegate : public RuntimeAPIDelegate {
  public:
   ShellRuntimeAPIDelegate();
   ~ShellRuntimeAPIDelegate() override;
 
   // RuntimeAPIDelegate implementation.
   void AddUpdateObserver(UpdateObserver* observer) override;
   void RemoveUpdateObserver(UpdateObserver* observer) override;
-  base::Version GetPreviousExtensionVersion(
-      const Extension* extension) override;
   void ReloadExtension(const std::string& extension_id) override;
   bool CheckForUpdates(const std::string& extension_id,
                        const UpdateCheckCallback& callback) override;
   void OpenURL(const GURL& uninstall_url) override;
   bool GetPlatformInfo(api::runtime::PlatformInfo* info) override;
   bool RestartDevice(std::string* error_message) override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ShellRuntimeAPIDelegate);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_SHELL_BROWSER_SHELL_RUNTIME_API_DELEGATE_H_