fix: avoid crash after upgrade on Linux

[cptpcrd]

Description of Change

Don't perform the "known executable" check on Linux if /proc/self/exe is going to be executed.

If the executable has been unlinked -- e.g. by the system package manager to perform an upgrade of an Electron-based app -- then executing /proc/self/exe will still work to launch copies of the same program since it is a "magic link" (see symlink(7)). However, this check breaks: readlink("/proc/self/exe") returns a fake path like /usr/lib/electron28/electron (deleted) which does not actually exist, so base::MakeAbsoluteFilePath fails to resolve the path and instead returns an empty string. This in turn causes the CHECK_EQ a few lines down to fail, and Electron crashes.

I think this is responsible for the crashes mentioned in #27804 and #33315.

Reproduction instructions for the crash (on Linux)

1. Download a copy of Electron to a temporary directory, e.g: cd $(mktemp -d); wget https://github.com/electron/electron/releases/download/v28.1.4/electron-v28.1.4-linux-x64.zip; unzip electron-v28.1.4-linux-x64.zip
2. Run ./electron -i.
3. In a different terminal, cd to the same temporary directory and run rm ./electron.
4. In the original terminal, run b = new BrowserWindow(); b.toggleDevTools().
5. Electron crashes.

Checklist

• PR description included and stakeholders cc'd
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Fixed crash after upgrade on Linux.

[welcome]

💖 Thanks for opening this pull request! 💖

We use semantic commit messages to streamline the release process. Before your pull request can be merged, you should update your pull request title to start with a semantic prefix.

Examples of commit messages with semantic prefixes:

• fix: don't overwrite prevent_default if default wasn't prevented
• feat: add app.isPackaged() method
• docs: app.isDefaultProtocolClient is now available on Linux

Things that will help get your PR across the finish line:

• Follow the JavaScript, C++, and Python coding style.
• Run npm run lint locally to catch formatting errors earlier.
• Document any user-facing changes you've made following the documentation styleguide.
• Include tests when adding/changing behavior.
• Include screenshots and animated GIFs whenever possible.

We get a lot of pull requests on this repo, so please be patient and we will get back to you as soon as we can.

[codebytere]

Small lint issue:

$ node ./script/lint.js && npm run lint:docs
shell/browser/electron_browser_client.cc:463:  (cpplint) If/else bodies with multiple statements require braces  [readability/braces] [4]
Total errors found: 1

[cptpcrd]

@codebytere are there any other changes you'd like to see here?

[zcbenz]

Can you rebase on latest main? Which should be able to fix the Windows CI failure.

[cptpcrd]

It's a bit unclear to me why the Linux/mac builds failed.

[release-clerk]

Release Notes Persisted

Fixed crash after upgrade on Linux.

[welcome]

Congrats on merging your first pull request! 🎉🎉🎉

[trop]

I have automatically backported this PR to "31-x-y", please check out #42062

[trop]

I have automatically backported this PR to "28-x-y", please check out #42063

[trop]

I have automatically backported this PR to "30-x-y", please check out #42064

[trop]

I have automatically backported this PR to "29-x-y", please check out #42065