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

chrome/browser/ui/search_engines/edit_search_engine_controller.h

Index: chrome/browser/ui/search_engines/edit_search_engine_controller.h
diff --git a/chrome/browser/ui/search_engines/edit_search_engine_controller.h b/chrome/browser/ui/search_engines/edit_search_engine_controller.h
index b1d988d74a41a0f057c5a31c44544db67a1fabb7..6163d8f3703734bcfd577929755b4dcd372ea3b8 100644
--- a/chrome/browser/ui/search_engines/edit_search_engine_controller.h
+++ b/chrome/browser/ui/search_engines/edit_search_engine_controller.h
@@ -33,6 +33,15 @@ class EditSearchEngineControllerDelegate {
 // 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,