Add missing IWYU message_loop.h includes.

components/password_manager/content/renderer/credential_manager_client_browsertest.cc

 // Copyright 2014 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 "components/password_manager/content/renderer/credential_manager_client.h"
 
 #include <stdint.h>
 
 #include <memory>
 #include <tuple>
 #include <utility>
 
 #include "base/location.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "content/public/renderer/render_frame.h"
 #include "content/public/renderer/render_view.h"
 #include "content/public/test/render_view_test.h"
 #include "mojo/public/cpp/bindings/binding_set.h"
 #include "services/service_manager/public/cpp/interface_provider.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/WebKit/public/platform/WebCredential.h"
@@ skipping 219 matching lines @@
 
   EXPECT_FALSE(callback_succeeded());
   EXPECT_TRUE(callback_errored());
   EXPECT_FALSE(credential_);
   EXPECT_EQ(blink::WebCredentialManagerError::
                 kWebCredentialManagerPasswordStoreUnavailableError,
             error_);
 }
 
 }  // namespace password_manager