Fix base::GetNativeLibraryName() for Mac.

base/native_library_ios.mm

 // Copyright (c) 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/native_library.h"
 
 #include "base/logging.h"
 
+#include "base/strings/string_util.h"
+
 namespace base {
 
 std::string NativeLibraryLoadError::ToString() const {
   return message;
 }
 
 // static
 NativeLibrary LoadNativeLibrary(const base::FilePath& library_path,
                                 NativeLibraryLoadError* error) {
   NOTIMPLEMENTED();
   if (error)
     error->message = "Not implemented.";
   return nullptr;
 }
 
 // static
 void UnloadNativeLibrary(NativeLibrary library) {
   NOTIMPLEMENTED();
   DCHECK(!library);
 }
 
 // static
 void* GetFunctionPointerFromNativeLibrary(NativeLibrary library,
                                           StringPiece name) {
   NOTIMPLEMENTED();
   return nullptr;
 }
 
 // static
-string16 GetNativeLibraryName(StringPiece16 name) {
+std::string GetNativeLibraryName(StringPiece name) {
+  DCHECK(IsStringASCII(name));
   return name.as_string();
 }
 
 }  // namespace base