Electron Releases

Description of Change

Fixes #54112.

Here's a demo where the only change is this PR applied.
-400ms saved from the launch time!

Content asks the embedder where to keep the GPU shader disk caches and only registers a cache for the handles that have a directory. ElectronBrowserClient never answered, so every shader Skia compiles for an app's UI is dropped on its way to disk and compiled again on the next launch.

flowchart LR
  A["GrShaderCache::store"] --> B["StoreBlobToDisk(kGrShaderGpuDiskCacheHandle)"]
  B --> C{"GetGrShaderDiskCacheDirectory()"}
  C -->|"Chrome: User Data\\GrShaderCache"| D["persisted, loaded next launch ✅"]
  C -->|"Electron: default, empty"| E["no cache for the handle → dropped ❌"]

• content/browser/gpu/gpu_disk_cache_factory.cc maps kDisplayCompositorGpuDiskCacheHandle → GetShaderDiskCacheDirectory(), kGrShaderGpuDiskCacheHandle → GetGrShaderDiskCacheDirectory(), kGraphiteDawnGpuDiskCacheHandle → GetGraphiteDawnDiskCacheDirectory(); gpu_process_host.cc uses GetGPUPersistentCacheDirectory() where features::kGpuPersistentCache is on (non-Windows).
• gpu/ipc/service/gpu_channel_manager.cc: StoreShader always targets kGrShaderGpuDiskCacheHandle. The per-renderer GPUCache Electron apps do have is gles2::ProgramCache (WebGL programs) — which is why VS Code's has ~1,200 entries and a non-WebGL app's has 0.
• This returns the same four directories Chrome does (chrome_content_browser_client.cc), rooted at sessionData next to GPUCache, Cache and the rest. Like those, sessionData has to be set before ready; the factory is created in BrowserMainLoop after the main script has run.

Prior art: Chrome has shipped exactly these directories for years; the on-disk format, prefix keying, corruption handling (kClearGrShaderDiskCacheOnInvalidPrefix, crbug 1442633) and clearStorageData({ storages: ['shadercache'] }) all already exist and apply unchanged.

Measured on Windows 11 / Intel Iris Xe / ANGLE D3D11, first raster of a window that paints text, rounded rects and shadows, --trace-startup:

base::FilePath ElectronBrowserClient::GetGrShaderDiskCacheDirectory() {
  return GpuCacheDirectory(FILE_PATH_LITERAL("GrShaderCache"));
}

Repro: https://gist.github.com/Hona/0ba82a4c26cc576cb4caeebc3f4ec746 (loads a page, waits 10 s, prints which shader caches exist under sessionData and their entry counts).

Checklist

• I have built and tested this change — Windows build in progress; the "after" column will be filled in from it
• I have filled out the PR description
• I have reviewed and verified the changes — drafted with Claude (see commit trailer), reviewed line by line against the Chromium 155 ContentBrowserClient signatures and ChromeContentBrowserClient's implementations
• npm test passes
• relevant API documentation, tutorials, and examples are updated and follow the documentation style guide — sessionData now mentions compiled GPU shaders
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, past tense, and no longer than 80 characters.

Release Notes

Notes: Fixed GPU shaders compiled by Skia not being cached between launches.