[LSC] Replace base::string16 with std::u16string in //chrome/browser/ui

This change replaces base::string16 with std::u16string in
//chrome/browser/ui.

Reproduction steps:
$ git grep -lw 'base::string16' chrome/browser/ui | \
      xargs sed -i 's/\bbase::string16\b/std::u16string/g'
$ git cl format

Bug: 1184339
Change-Id: Ie4678628a9041f5e896d4b3bb7c6a2fbb0e0afd2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2752286
Auto-Submit: Jan Wilken Dörrie <[email protected]>
Commit-Queue: Jan Wilken Dörrie <[email protected]>
Owners-Override: Jan Wilken Dörrie <[email protected]>
Reviewed-by: danakj <[email protected]>
Cr-Commit-Position: refs/heads/master@{#862038}
diff --git a/chrome/browser/ui/webui/components/components_handler.h b/chrome/browser/ui/webui/components/components_handler.h
index 4f2f38f..6b5522d 100644
--- a/chrome/browser/ui/webui/components/components_handler.h
+++ b/chrome/browser/ui/webui/components/components_handler.h
@@ -43,8 +43,8 @@
   void OnEvent(Events event, const std::string& id) override;
 
  private:
-  static base::string16 ComponentEventToString(Events event);
-  static base::string16 ServiceStatusToString(
+  static std::u16string ComponentEventToString(Events event);
+  static std::u16string ServiceStatusToString(
       update_client::ComponentState state);
 
   std::unique_ptr<base::ListValue> LoadComponents();