[LSC] Replace base::string16 with std::u16string in //cr/browser/[h-z]*

This change replaces base::string16 with std::u16string in
//chrome/browser/[h-z]*.

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

Bug: 1184339
Change-Id: Ibb73866fc5c9171ba525a1fd7dc9b4b7e619468d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2752228
Commit-Queue: Jan Wilken Dörrie <[email protected]>
Owners-Override: Peter Kasting <[email protected]>
Reviewed-by: Peter Kasting <[email protected]>
Cr-Commit-Position: refs/heads/master@{#862036}
diff --git a/chrome/browser/recovery/recovery_install_global_error.h b/chrome/browser/recovery/recovery_install_global_error.h
index eb31abe..e46c4cd2a 100644
--- a/chrome/browser/recovery/recovery_install_global_error.h
+++ b/chrome/browser/recovery/recovery_install_global_error.h
@@ -30,19 +30,19 @@
   Severity GetSeverity() override;
   bool HasMenuItem() override;
   int MenuItemCommandID() override;
-  base::string16 MenuItemLabel() override;
+  std::u16string MenuItemLabel() override;
   ui::ImageModel MenuItemIcon() override;
   void ExecuteMenuItem(Browser* browser) override;
   bool HasBubbleView() override;
   bool HasShownBubbleView() override;
   void ShowBubbleView(Browser* browser) override;
   bool ShouldCloseOnDeactivate() const override;
-  base::string16 GetBubbleViewTitle() override;
-  std::vector<base::string16> GetBubbleViewMessages() override;
-  base::string16 GetBubbleViewAcceptButtonLabel() override;
+  std::u16string GetBubbleViewTitle() override;
+  std::vector<std::u16string> GetBubbleViewMessages() override;
+  std::u16string GetBubbleViewAcceptButtonLabel() override;
   bool ShouldShowCloseButton() const override;
   bool ShouldAddElevationIconToAcceptButton() override;
-  base::string16 GetBubbleViewCancelButtonLabel() override;
+  std::u16string GetBubbleViewCancelButtonLabel() override;
   void OnBubbleViewDidClose(Browser* browser) override;
   void BubbleViewAcceptButtonPressed(Browser* browser) override;
   void BubbleViewCancelButtonPressed(Browser* browser) override;