Adding WebThread and new BlinkPlatformImpl for utility thread.

content/utility/utility_blink_platform_impl.cc

+// Copyright 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 "content/utility/utility_blink_platform_impl.h"
+
+namespace content {
+
+UtilityBlinkPlatformImpl::UtilityBlinkPlatformImpl()
+    : main_thread_(new WebThreadImplForUtilityThread()) {
+}
+
+UtilityBlinkPlatformImpl::~UtilityBlinkPlatformImpl() {
+}
+
+blink::WebThread* UtilityBlinkPlatformImpl::currentThread() {
+  if (main_thread_->isCurrentThread())
+    return main_thread_.get();
+  return BlinkPlatformImpl::currentThread();
+}
+
+}  // namespace content