[Extensions] Update extensions UI to observe events and add test

chrome/browser/extensions/api/developer_private/extension_info_generator.h

 // Copyright 2015 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 CHROME_BROWSER_EXTENSIONS_API_DEVELOPER_PRIVATE_EXTENSION_INFO_GENERATOR_H_
 #define CHROME_BROWSER_EXTENSIONS_API_DEVELOPER_PRIVATE_EXTENSION_INFO_GENERATOR_H_
 
 #include "chrome/common/extensions/api/developer_private.h"
 
 namespace content {
 class BrowserContext;
 }
 
 namespace extensions {
 class ErrorConsole;
 class Extension;
 class ExtensionPrefs;
 class ExtensionSystem;
 class WarningService;
 
 // Generates the developerPrivate api's specification for ExtensionInfo.
 class ExtensionInfoGenerator {
  public:
   using ExtensionInfoList =
       std::vector<linked_ptr<api::developer_private::ExtensionInfo>>;
 
   explicit ExtensionInfoGenerator(content::BrowserContext* context);
   ~ExtensionInfoGenerator();
 
-  // Return the ExtensionInfo for a given |extension| and |state|.
+  // Returns the ExtensionInfo for a given |extension| and |state|.
   scoped_ptr<api::developer_private::ExtensionInfo> CreateExtensionInfo(
       const Extension& extension,
       api::developer_private::ExtensionState state);
+  // Returns an ExtensionInfo for the given |extension_id|, if the extension
+  // can be found.
+  scoped_ptr<api::developer_private::ExtensionInfo> CreateExtensionInfo(
+      const std::string& id);
 
-  // Return a collection of ExtensionInfos, optionally including disabled and
+  // Returns a collection of ExtensionInfos, optionally including disabled and
   // terminated.
   ExtensionInfoList CreateExtensionsInfo(bool include_disabled,
                                          bool include_terminated);
 
  private:
   // Various systems, cached for convenience.
   content::BrowserContext* browser_context_;
   ExtensionSystem* extension_system_;
   ExtensionPrefs* extension_prefs_;
   WarningService* warning_service_;
   ErrorConsole* error_console_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionInfoGenerator);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_DEVELOPER_PRIVATE_EXTENSION_INFO_GENERATOR_H_