Fix DCHECK failure and add unittest for BlimpSystemURLContextGetter.

blimp/engine/app/blimp_system_url_request_context_getter_unittest.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/blimp_system_url_request_context_getter.h"
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "content/public/test/test_browser_thread_bundle.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace blimp {
+namespace engine {
+
+namespace {
+class BlimpSystemURLRequestContextGetterTest : public testing::Test {
+ public:
+  BlimpSystemURLRequestContextGetterTest()
+      : system_url_request_context_getter_(
+            new BlimpSystemURLRequestContextGetter()) {}
+
+ protected:
+  content::TestBrowserThreadBundle thread_bundle_;
+  scoped_refptr<BlimpSystemURLRequestContextGetter>
+      system_url_request_context_getter_;
+};
+
+TEST_F(BlimpSystemURLRequestContextGetterTest, GetURLRequestContext) {
+  ASSERT_NE(nullptr,
+            system_url_request_context_getter_->GetURLRequestContext());
+}
+
+}  // namespace
+
+}  // namespace engine
+}  // namespace blimp