Drawer with keepMounted has incorrect aria-hidden value

[roosmaa]

When using the following snippet:

<Drawer
    variant="temporary"
    ModalProps={{
        keepMounted: true
    }}
    {..other}
/>

The aria-hidden attribute logic gets applied incorrectly.

• This is a v1.x issue.
• I have searched the issues of this repository and believe that this is not a duplicate.

Expected Behavior

When the drawer is open, the content gets aria-hidden="true" and drawer modal gets aria-hidden="false".
When drawer is closed, the content gets aria-hidden="false" and drawer modal gets aria-hidden="true".

Current Behavior

When the drawer is open, the both the content and drawer modal get aria-hidden="true" (resulting in a screen reader stating that there is no content).
When drawer is closed, both the content and drawer modal get aria-hidden="false".

Steps to Reproduce

Link: https://material-ui.com/

1. Open drawer
2. Open dev-tools
3. Check aria-hidden attributes for drawer modal & content
4. Close drawer
5. Recheck aria-hidden attributes for drawer modal & content

Context

To make temporary drawer apps friendly to screen readers.

Your Environment

Tech	Version
Material-UI	v1.4.2
React	v16.4.0
TypeScript	3.0.1
etc.