Electron Releases

Release build (is_official_build=true, dcheck_always_on=false), x64 Linux, 24 cold samples/build, measured from process spawn:

The 4.4 MB snapshot adds ~4.6 ms of deserialize on the pre-ready path (already netted in). The first-JS → ready segment is Chromium browser-init, which this doesn't touch, so it's flat — the win is the Node/Electron bootstrap.

The snapshot extends the same V8 startup snapshot the rest of the process already uses (snapshot_blob.bin), so the read-only heap stays shared and V8's one-snapshot-per-process invariant holds.

node_snapshot (a separate source_set in third_party/electron_node:unofficial.gni) provides the strong SnapshotBuilder::GetEmbeddedSnapshotData over a now-weak no-op stub. electron_lib deps it, so the shipped framework links the real snapshot while node_mksnapshot (which links only libnode + the weak stub) does not — avoiding the GN dependency cycle that v8_snapshot_toolchain == default_toolchain would otherwise force on native builds. Snapshot generation is gated to native builds.

Browser-process wiring:

• javascript_environment.cc — when the embedded snapshot is present, CreateIsolateHolder feeds its blob + external references into the isolate CreateParams. The ctor skips node::NewContext; the main context is materialized from the snapshot inside node::CreateEnvironment.
• electron_browser_main_parts.cc — passes an empty context to Initialize/CreateEnvironment in the snapshot path, then enters the deserialized context after.
• node_bindings.cc — CreateEnvironment defers context-dependent setup until the snapshot's main context exists; CreateIsolateData receives the snapshot's per-isolate data; LoadEnvironment merges the build-time electron/js2c/* cache with the snapshot's per-builtin cache.

• Release build boots; sandboxed BrowserWindow smoke test (loads a data URL, runs JS, returns the Electron UA) passes — child processes are unaffected by the browser-only snapshot.
• spec/api-js2c-code-cache-spec.ts from #51697 passes: the browser process's browser_init/node_init build-time code caches are consumed (verified via NODE_DEBUG_NATIVE=CODE_CACHE — both is accepted). This required generating the browser cache against the snapshot's isolate (see "Browser js2c code cache" below); the other flavors are byte-identical to #51697.

A SnapshotCreator-produced snapshot owns a unique read-only-heap checksum that matches no standalone blob (not the v8_context_snapshot, not the snapshot_blob.bin it extends). V8's code-cache key embeds that checksum, so the build-time js2c cache for browser_init/node_init is only valid if it's generated against the shipped snapshot's isolate. A dedicated electron_natives_codecache_snapshot host tool links the real node_snapshot and compiles those bundles via GetEmbeddedSnapshotData() + InitializeIsolateParams(), so the cache's read-only checksum matches the runtime browser isolate by construction. The four non-browser flavors keep using the v8 context snapshot.