Remove mojo::String.

content/browser/mime_registry_impl.cc

Index: content/browser/mime_registry_impl.cc
diff --git a/content/browser/mime_registry_impl.cc b/content/browser/mime_registry_impl.cc
index a7016ad2a90ef0676c5b2a7edef02b2696f21076..09e6aebe8841f02be93cb1a16d79c45c50760cdf 100644
--- a/content/browser/mime_registry_impl.cc
+++ b/content/browser/mime_registry_impl.cc
@@ -30,7 +30,7 @@ void MimeRegistryImpl::GetMimeTypeFromExtension(
   DCHECK_CURRENTLY_ON(BrowserThread::FILE);
   std::string mime_type;
   net::GetMimeTypeFromExtension(
-      mojo::String(extension).To<base::FilePath::StringType>(), &mime_type);
+      base::FilePath::FromUTF8Unsafe(extension).value(), &mime_type);
   callback.Run(mime_type);
 }