Remove unnecessary conversion to/from WebString

Change-Id: Ibed70c17d5ba2bb9a9073e5b6174896744064a80
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1619689
Commit-Queue: Daniel Bratell <bratell@opera.com>
Auto-Submit: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#661325}

third_party/blink/renderer/core/frame/web_frame_serializer_impl.cc

@@ -101,12 +101,11 @@ namespace blink {
 namespace {
 
 // Generate the default base tag declaration.
-String GenerateBaseTagDeclaration(const WebString& base_target) {
+String GenerateBaseTagDeclaration(const String& base_target) {
   // TODO(yosin) We should call |FrameSerializer::baseTagDeclarationOf()|.
   if (base_target.IsEmpty())
     return String("<base href=\".\">");
-  String base_string = "<base href=\".\" target=\"" +
-                       static_cast<const String&>(base_target) + "\">";
+  String base_string = "<base href=\".\" target=\"" + base_target + "\">";
   return base_string;
 }