Cannot use mouse wheel within a PDF document that is being displayed in a frame

[Brave_user]

Description of the issue: Cannot use mouse wheel within a PDF document that is being displayed in a frame

Steps to Reproduce (add as many as necessary): 1. 2. 3.

1. I only encountered that problem using the webmail interface at fastmail.com.
2. Log in to fastmail.com.
3. Open an email with a PDF attachment.
4. Click the PDF attachment.
5. After PDF document has opened try to scroll using your mouse wheel.

Actual Result (gifs and screenshots are welcome!): Cannot scroll

Expected result: Can scroll

Reproduces how often: Every time

Operating System and Brave Version(See the About Brave page in the main menu): Version 0.63.48 Chromium: 74.0.3729.108 and Windows 6.1.7601

Additional Information: I have only encountered this issue on fastmail.com. So you probably can only reproduce it with a Fastmail.com account. The issue is the same on different PCs.
==> Issue shows if you open a PDF document on a Fastmail website with frames. See screenshot does_not_scroll.png

==> Issue does not show if PDF document is downloaded and opens within Brave without any frames. See screenshot does_scroll.png

[Brave_user]

I confirmed it is a Brave related issue. Firefox also uses PDF.js to render PDF documents. No problem there. I also tried a couple of other browsers, some are using PDF.js and some the original Adobe plugin. All browsers I tried let me scroll through a PDF document.

The only browser with this issue is Brave. Prior versions worked without any problems.