Check browser support before instantiating controllers

[mmermerkaya]

Checks browser support before instantiating messaging service controllers and fixes some tests.

I think it's better to let the developer know that Messaging will not work as soon as possible, instead of instantiating a controller without an issue and then throwing an error as soon as they try to use it.

This also prevents issues such as #658 by making sure we don't call any unsupported methods by accident.

This can break users who were not checking browser support before calling firebase.messaging(), so it should go to the v5 branch.

[googlebot]

So there's good news and bad news.

👍 The good news is that everyone that needs to sign a CLA (the pull request submitter and all commit authors) have done so. Everything is all good there.

😕 The bad news is that it appears that one or more commits were authored or co-authored by someone other than the pull request submitter. We need to confirm that all authors are ok with their commits being contributed to this project. Please have them confirm that here in the pull request.

Note to project maintainer: This is a terminal state, meaning the cla/google commit status will not change from this state. It's up to you to confirm consent of the commit author(s) and merge this pull request when appropriate.

[mmermerkaya]

I changed the base to v5/master, but that got @googlebot a bit confused. All commits in this PR are mine.

[gauntface]

I'm still against this PR without an API review for the permission change.

[mmermerkaya]

Permission change?

Sure, I can send it to API review.

[googlebot]

CLAs look good, thanks!

[mmermerkaya]

Went through API review, implemented requested changes.