版本（versions）：
react@16.0.0
react-dom@16.0.0

描述（description）：
给父级别绑定 onMouseEnter 事件。在首次渲染后，鼠标移入新渲染进去的子元素会触发父元素的 onMouseEnter 事件。

示例（demo）：

```js
import React, {Component} from 'react';

class Demo extends Component {
    constructor(prop) {
        super(prop);
        this.enter = this.enter.bind(this)
        this.state = {
            flag: false
        }
    }
    enter(event) {
        console.log(event.nativeEvent);
        console.log("enter")
    }
    click() {
        this.setState({flag:!this.state.flag})
    }
    render() {
        let old = {
            height: "100px",
            width: "100px",
            border: "1px solid #6dbbff"
        };
        let aa = {
            height: "100px",
            width: "100px",
            border: "1px solid red"
        };
        let content = {
            border: "1px solid black",
            display: "flex",
            padding:"10px"
        }
        return(
            <div>
                <div style={content} onMouseEnter={this.enter}>
                    {this.state.a}
                    <div style={old}>old</div>
                    <div style={aa}>old</div>
                    {this.state.flag && <div style={aa}>new</div>}
                </div>
                <button onClick={this.click.bind(this)}>点我（click me）</button>
            </div>
        )
    }
}
```
instB = getParent(instB);
    depthB--;
  }
  
  var depth = depthA;
  while (depth--) {
    if (instA === instB || instA === instB.alternate) {
      return instA;
    }
    instA = getParent(instA);
    instB = getParent(instB);
  }
  return null;
}
/**
 * Return if A is an ancestor of B.
 */
function isAncestor(instA, instB) {
  while (instB) {
    if (instA === instB || instA === instB.alternate) {
      return true;
    }
    instB = getParent(instB);
  }
  return false;
}
/**
 * Return the parent instance of the passed-in instance.
 */
function getParentInstance(inst) {