[LSC] Replace base::string16 with std::u16string in //{chrome*,content}

This change replaces base::string16 with std::u16string in //chrome,
//chromecast, //chromeos and //content.

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

Bug: 1184339
Change-Id: I8fae0ab25b5d9bf1cb416ae5f47d7f680fb8f3ea
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2752229
Commit-Queue: Jan Wilken Dörrie <[email protected]>
Commit-Queue: Daniel Cheng <[email protected]>
Owners-Override: Daniel Cheng <[email protected]>
Auto-Submit: Jan Wilken Dörrie <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Cr-Commit-Position: refs/heads/master@{#862152}
diff --git a/content/browser/renderer_host/navigation_controller_impl.cc b/content/browser/renderer_host/navigation_controller_impl.cc
index 9af368c..2160142 100644
--- a/content/browser/renderer_host/navigation_controller_impl.cc
+++ b/content/browser/renderer_host/navigation_controller_impl.cc
@@ -561,7 +561,7 @@
   auto entry = std::make_unique<NavigationEntryImpl>(
       nullptr,  // The site instance for tabs is sent on navigation
                 // (WebContents::GetSiteInstance).
-      url_to_load, referrer, initiator_origin, base::string16(), transition,
+      url_to_load, referrer, initiator_origin, std::u16string(), transition,
       is_renderer_initiated, blob_url_loader_factory);
   entry->SetVirtualURL(virtual_url);
   entry->set_user_typed_url(virtual_url);
@@ -1549,7 +1549,7 @@
     new_entry = std::make_unique<NavigationEntryImpl>(
         rfh->GetSiteInstance(), params.url, Referrer(*params.referrer),
         initiator_origin,
-        base::string16(),  // title
+        std::u16string(),  // title
         params.transition, request->IsRendererInitiated(),
         nullptr);  // blob_url_loader_factory