Reland: Implement Aura side of unified touch text selection for contents

ui/touch_selection/touch_selection_menu_runner.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 "ui/touch_selection/touch_selection_menu_runner.h"
+
+namespace ui {
+namespace {
+
+TouchSelectionMenuRunner* g_touch_selection_menu_runner = nullptr;
+
+}  // namespace
+
+TouchSelectionMenuRunner::~TouchSelectionMenuRunner() {
+  g_touch_selection_menu_runner = nullptr;
+}
+
+TouchSelectionMenuRunner* TouchSelectionMenuRunner::GetInstance() {
+  return g_touch_selection_menu_runner;
+}
+
+TouchSelectionMenuRunner::TouchSelectionMenuRunner() {
+  g_touch_selection_menu_runner = this;
+}
+
+}  // namespace ui