Add UMA for window.external.AddSearchProvider (Chrome side).

chrome/browser/ui/search_engines/edit_search_engine_controller.h

 // Copyright (c) 2012 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_UI_SEARCH_ENGINES_EDIT_SEARCH_ENGINE_CONTROLLER_H_
 #define CHROME_BROWSER_UI_SEARCH_ENGINES_EDIT_SEARCH_ENGINE_CONTROLLER_H_
 
 #include <string>
 
 #include "base/strings/string16.h"
@@ skipping 15 matching lines @@
                                const std::string& url) = 0;
 
  protected:
   virtual ~EditSearchEngineControllerDelegate() {}
 };
 
 // EditSearchEngineController provides the core platform independent logic
 // for the Edit Search Engine dialog.
 class EditSearchEngineController {
  public:
+  // An enum to match the AddSearchProvider UMA enum.

[Mark P, 2015/10/19 21:53:43]

please explicitly do = 0, = 1, etc. (except for NUM_ACTIONS)
and also state that these items should not be reordered or renumbered; all new
items should be added just before NUM_ACTIONS

[Evan Stade, 2015/10/19 22:55:15]

Done.

Out of curiosity, what's the reasoning for being explicit about the values?
Doesn't the C++ standard guarantee these values anyway (even the = 0 should be
unnecessary)?

[Mark P, 2015/10/20 19:37:28]

Yes, you're right.  However in my experience, being explicit about the values
makes it more obvious when someone else modifies the code to do something wrong.
 e.g., without explicit =whatever, I've seen people add new enums in the middle
(even with the UMA comment warning), and the code reviewer hasn't caught the
issue.  I've never seen this happen with explicit =whatever all the way down.

+  enum EditSearchEngineActions {
+    ADD_SEARCH_PROVIDER_CALLED = 0,
+    CONFIRMATION_DIALOG_SHOWN,
+    CONFIRMATION_DIALOG_CONFIRMED,
+    CONFIRMATION_DIALOG_CANCELLED,
+    NUM_EDIT_SEARCH_ENGINE_ACTIONS
+  };
+
   // The |template_url| and/or |edit_keyword_delegate| may be NULL.
   EditSearchEngineController(
       TemplateURL* template_url,
       EditSearchEngineControllerDelegate* edit_keyword_delegate,
       Profile* profile);
   ~EditSearchEngineController() {}
 
   // Returns true if the value of |title_input| is a valid search engine name.
   bool IsTitleValid(const base::string16& title_input) const;
 
@@ skipping 35 matching lines @@
   // success to add/modify the entry.  May be NULL.
   EditSearchEngineControllerDelegate* edit_keyword_delegate_;
 
   // Profile whose TemplateURLService we're modifying.
   Profile* profile_;
 
   DISALLOW_COPY_AND_ASSIGN(EditSearchEngineController);
 };
 
 #endif  // CHROME_BROWSER_UI_SEARCH_ENGINES_EDIT_SEARCH_ENGINE_CONTROLLER_H_