Do extra check to be sure ngDevMode is defined - #36055

Also please change the git commit message to:

fix(core): guard reading of global `ngDevMode` for undefined.

When reading globals such as `ngDevMode` the read should be guarded by `typeof ngDevMode` otherwise it will throw if not defined in `"use strict"` mode.

I know resources are limited, but any chance someone could get the final review done?

Hi @mcalmus, thanks for creating this PR.

Could you please perform a couple updates:

• squash commits into a single commit (keeping the one that starts with fix(core): ...)
• add a comment in the code to describe why there is an additional typeof ngDevMode check even though we set it in ngDevModeResetPerfCounters as Misko requested in Do extra check to be sure ngDevMode is defined #36055 (comment) (use the content from the commit body).

Thank you.

Done

Thanks for the update @mcalmus. I looked at the comment and I think it'd be great to expand it to provide more context. It's still a bit unclear why this extra check is needed. I agree that this approach is much safer, but it's not clear what the main reason is and having a detailed comment would help a lot. Feel free to share what the problem was in your use-case and I can help put together a comment that we can add to the code. Thank you.

@AndrewKushnir Here is my comment in the original issue: #31595 (comment)
Essentially, I was porting legacy code that had an included .js file with a var named 'global'. I had declared this in global.d.ts. When running the app in any browser but Chrome it would blow up with an "undefined" error.

Clearly I rushed that comment, even with a typo. I guess I should have said "if defined globally elsewhere" or something like that. In any event it has been removed.

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CLAs look good, thanks!

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Hi @mcalmus, thanks for applying the changes, the code looks good.

Could you please squash all commits in 1 commit and rebase this PR on top of the current master?

Thank you.

Presubmit.

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