Convert from base::{LazyInstance,Singleton} to base::NoDestructor

The class base::NoDestructor is a simpler way to define a static
global value (aka a singleton) than base::{LazyInstance,Singleton}
and is the recommended pattern to use.

The changes were automated using a custom one-shot script, then
fine tuned by hand (to remove unnecessary classes, ...).

This fixes usages in src/ios/chrome/browser/web_state_list.

This CL was uploaded by git cl split.

Bug: none
Change-Id: I5f3110c566d3d0dfa11ffe801a7622d4d96400a2
Reviewed-on: https://chromium-review.googlesource.com/c/1411695Reviewed-by: David Roger <droger@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622977}

ios/chrome/browser/web_state_list/web_usage_enabler/web_state_list_web_usage_enabler_factory.h

@@ -6,13 +6,9 @@
 #define IOS_CHROME_BROWSER_WEB_STATE_LIST_WEB_USAGE_ENABLER_WEB_STATE_LIST_WEB_USAGE_ENABLER_FACTORY_H_
 
 #include "base/macros.h"
+#include "base/no_destructor.h"
 #include "components/keyed_service/ios/browser_state_keyed_service_factory.h"
 
-namespace base {
-template <typename T>
-struct DefaultSingletonTraits;
-}
-
 namespace ios {
 class ChromeBrowserState;
 }
@@ -32,8 +28,7 @@ class WebStateListWebUsageEnablerFactory
   static WebStateListWebUsageEnablerFactory* GetInstance();
 
  private:
-  friend struct base::DefaultSingletonTraits<
-      WebStateListWebUsageEnablerFactory>;
+  friend class base::NoDestructor<WebStateListWebUsageEnablerFactory>;
 
   WebStateListWebUsageEnablerFactory();
 

ios/chrome/browser/web_state_list/web_usage_enabler/web_state_list_web_usage_enabler_factory.mm

@@ -6,7 +6,7 @@
 
 #include <memory>
 
-#include "base/memory/singleton.h"
+#include "base/no_destructor.h"
 #include "components/keyed_service/ios/browser_state_dependency_manager.h"
 #include "ios/chrome/browser/browser_state/browser_state_otr_helper.h"
 #include "ios/chrome/browser/browser_state/chrome_browser_state.h"
@@ -27,7 +27,8 @@ WebStateListWebUsageEnablerFactory::GetForBrowserState(
 // static
 WebStateListWebUsageEnablerFactory*
 WebStateListWebUsageEnablerFactory::GetInstance() {
-  return base::Singleton<WebStateListWebUsageEnablerFactory>::get();
+  static base::NoDestructor<WebStateListWebUsageEnablerFactory> instance;
+  return instance.get();
 }
 
 WebStateListWebUsageEnablerFactory::WebStateListWebUsageEnablerFactory()