[Blimp] Adds blimp engine browser test framework and LoadUrl test.

blimp/engine/app/test_content_main_delegate.cc

+// 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.
+
+#include "blimp/engine/app/test_content_main_delegate.h"
+
+namespace blimp {
+namespace engine {
+namespace {
+TestContentMainDelegate* g_content_main_delegate = nullptr;
+}  // namespace
+
+TestContentMainDelegate::TestContentMainDelegate() {
+  DCHECK(!g_content_main_delegate);
+  g_content_main_delegate = this;
+}
+
+TestContentMainDelegate::~TestContentMainDelegate() {
+  DCHECK_EQ(this, g_content_main_delegate);
+  g_content_main_delegate = nullptr;
+}
+
+// static
+TestContentMainDelegate* TestContentMainDelegate::GetInstance() {
+  return g_content_main_delegate;
+}
+
+}  // namespace engine
+}  // namespace blimp