Coalesce warnings for deprecated lifecycle hooks and print single message after reconciliation (rather than one per component-type).

Relates to PR #12028 and [this comment](https://github.com/facebook/react/pull/12028#discussion_r162420575).
/**
 * Copyright (c) 2013-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @emails react-core
 */
'use strict';
let React;
let ReactDOM;
let ReactFeatureFlags;
let createReactClass;
describe('create-react-class-integration', () => {
  beforeEach(() => {
    ReactFeatureFlags = require('shared/ReactFeatureFlags');
    ReactFeatureFlags.warnAboutDeprecatedLifecycles = true;
    React = require('react');
    ReactDOM = require('react-dom');
    createReactClass = require('create-react-class/factory')(
      React.Component,
      React.isValidElement,
      new React.Component().updater,
    );
  });
  
  
  it('isMounted works', () => {
    const ops = [];