Fix missing symbols for pre-linking of the Cast sender library for iOS.

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"
+
+namespace base {
+
+std::string NativeLibraryLoadError::ToString() const {
+  return message;
+}
+
+// static
+NativeLibrary LoadNativeLibrary(const base::FilePath& library_path,
+                                NativeLibraryLoadError* error) {
+  return nullptr;
+}
+
+// static
+void UnloadNativeLibrary(NativeLibrary library) {
+  delete library;
+}
+
+// static
+void* GetFunctionPointerFromNativeLibrary(NativeLibrary library,
+                                          const char* name) {
+  return nullptr;
+}
+
+// static
+string16 GetNativeLibraryName(const string16& name) {
+  return name;
+}
+
+}  // namespace base