MatTreeModule broken when has target ES6

[vadjs]

Bug, feature request, or proposal:

bug

What is the expected behavior?

MatTreeModule should working correct when tsconfig has "target": "es6".

What is the current behavior?

If you set "target": "es6" in tsconfig and try to expand tree node you will get next error:
Cannot read property 'treeControl' of undefined

What are the steps to reproduce?

I reproduced bug in this repo: https://github.com/vadjs/material2-tree-bug
I've got TreeDemoModule from material2 repo and pasted it in clean angular-cli project.

What is the use-case or motivation for changing an existing behavior?

Working properly when when tsconfig has "target": "es6".

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

Angular 7.0.0, Material 7.0.0/7.0.1(probably earlier).

Is there anything else we should know?

[devversion]

See #14066

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