[Bug Report]iview3.0 introduces Tree components on demand, and how size sets up when it is introduced on demand.

[ycyucan]

Environment

ivew3.0

Reproduction link

https://github.com/iview/iview/issues/new

Steps to reproduce

import Tree form ‘iview’ Vue.component('Tree"，Tree)

What is expected?

怎么实现按需引入时候size 的设置

What is actually happening?

size报错

[iview-bot]

Translation of this issue:
Environment
Ivew3.0
Reproduction link
https://github.com/iview/iview/issues/new
Steps to reproduce
Import Tree form "iView" Vue.component ('Tree ", Tree)
What is expected?
How to implement size settings when required to be introduced
What is actually happening?
Size is wrong

[leafiy]

when using import on demand , always "TypeError: Cannot read property 'size' of undefined"
happens on import { *** } from 'iview' , not only Tree component

[leafiy]

there is temporary solution, add this line to main.js
Vue.prototype.$IVIEW = {}