[ios] Adds OmahaServiceProvider.

ios/public/provider/chrome/browser/omaha/test_omaha_service_provider.mm

+// Copyright 2016 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.
+
+#import "ios/public/provider/chrome/browser/omaha/test_omaha_service_provider.h"
+
+TestOmahaServiceProvider::TestOmahaServiceProvider() {}
+
+TestOmahaServiceProvider::~TestOmahaServiceProvider() {}
+
+GURL TestOmahaServiceProvider::GetUpdateServerURL() const {
+  return GURL();
+}
+
+std::string TestOmahaServiceProvider::GetApplicationID() const {
+  return std::string();
+}
+
+std::string TestOmahaServiceProvider::GetBrandCode() const {
+  return std::string();
+}
+
+void TestOmahaServiceProvider::AppendExtraAttributes(
+    const std::string& tag,
+    OmahaXmlWriter* writer) const {}