Add class for picture in picture window

[Crinax]

Description

Picture in picture mode window has no class. It make difficults to apply rules for window in such WM as Hyprland

Steps to Reproduce

1. Open any video in picture in picture mode
2. For hyprland run command hyprctl clients

Actual result:

Window no class only name

Expected result:

Has some class, for example: brave-pip or brave-picture-in-picture

Reproduces how often:

Easily reproduced

Brave version (brave://version info)

Brave: 1.65.133 Chromium: 124.0.6367.208 (Official build) unknown (64 bit)
Version: a719189e6a0245a6ce7fab3ddc637e8bd75aed08
OS: Linux

Version/Channel Information:

• Can you reproduce this issue with the current release? [Yes]
• Can you reproduce this issue with the beta channel? [Not tried]
• Can you reproduce this issue with the nightly channel? [Not tried]

Other Additional Information:

Miscellaneous Information: