Add Electron Fiddle for Win 24H2 DWM/MPO repro testing

[jjeff]

Summary

Adds an electron-fiddle/ directory containing a minimal Electron Fiddle that loads the gh-pages reproduction page (https://spaceagetv.github.io/chromium-gpu-bug/) inside a BrowserWindow. A clearly labeled FLAGS block at the top of main.js lets engineers toggle:

• --use-angle (d3d9 / gl / warp / default)
• --gpu-preference (low-power / high-performance / default)
• --force_low_power_gpu
• --disable-features=DirectCompositionVideoOverlays
• --disable-features=D3D11VideoDecoder

so Electron's behavior can be compared against Chrome on identical hardware. By default everything is commented out — that matches a stock Electron app and is the baseline you want to compare against Chrome.

How to load it

Clone the repo and in Electron Fiddle use File → Open Fiddle… pointed at the electron-fiddle/ directory. (You can also still load it via electron-fiddle://gist/c82631380f573e3278d864c57fa75df0.)

Relationship to the existing gist

This Fiddle was previously published as gist c82631380f573e3278d864c57fa75df0. After this PR merges the gist becomes redundant — leaving whether to delete it to maintainer discretion. The README inside electron-fiddle/ already points to this directory as the canonical location going forward.

Independent of PR #1

This change is independent of #1 (the improve-h264-repro-with-audio test-video update) — both can land in either order without conflict.

Test plan

• Clone the branch
• Open electron-fiddle/ in Electron Fiddle and click Run
• Confirm the gh-pages repro page loads in the BrowserWindow
• Uncomment one FLAGS line (e.g. use-angle d3d9), Run, confirm it took effect via DevTools