Shared Pinned Tabs are attempted to be created for PWA windows

[petemill]

Description

This is only guarded with a DCHECK (which causes a crash in debug builds). In release builds it causes pinned tabs to be created on PWA-tabbed windows, and some crashes for non-PWA-tabbed windows.

Steps to Reproduce

1. Enable shared pinned tabs flag
2. Create a PWA

Actual result:

In Debug: crash occurs

Expected result:

The PWA window is not considered for pinned tabs

Reproduces how often:

Easily in debug, crash sometimes in release

Brave version (brave://version info)

Version/Channel Information:

• Can you reproduce this issue with the current release?
• Can you reproduce this issue with the beta channel?
• Can you reproduce this issue with the nightly channel?

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields?
• Does the issue resolve itself when disabling Brave Rewards?
• Is the issue reproducible on the latest version of Chrome?

Miscellaneous Information: