Electron Releases

Root-cause fix for the corrupt profraw files behind microsoft/vscode#331672 (see #53064 for the 42-x-y profile restore and #53065 for the merge gate).

• In chrome_pgo_phase = 1 builds, sandboxed children write their counters through a file handle the browser hands them (CLANG_PROFILING_INSIDE_SANDBOX), and only do so when asked or on clean exit. Electron never asked: app.quit() quit the main loop, the sandbox job object killed any child still writing, and the truncated child_pool-*.profraw was dropped at merge. The loser is usually the benchmark renderer, so Blink ends up cold in the published profile. 42-x-y win-x64 lost this race 3/3 runs since 2026-08-02; main win-arm64's latest profile is partially hit.
• Mirror chrome/browser/lifetime/browser_shutdown.cc: at the start of Browser::Shutdown() call content::AskAllChildrenToDumpProfilingData() and run a nested loop until every child has flushed. Guarded by CLANG_PROFILING_INSIDE_SANDBOX && CLANG_PGO_PROFILING, so it compiles out of every shipping build.
• Verified the TU compiles with the current tree both with the flags off and with them forced on (object then references AskAllChildrenToDumpProfilingData). End-to-end check: a pgo-generation dispatch on this branch should yield 4 valid child_pool files for win-x64 with no file header is corrupt warnings in the Merge Profiles job.

Notes: none