Add traceback to unhandled promise rejections

[graingert]

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
Feature

What is the current behavior? (You can also link to an open issue here)
Console is filled with meaningless: Possibly unhandled rejection: {} errors

What is the new behavior (if this is a feature change)?
Console is filled with juicy traceback info.

Does this PR introduce a breaking change?
I don't think so

Please check if the PR fulfills these requirements

• The commit message follows our guidelines: https://github.com/angular/angular.js/blob/master/CONTRIBUTING.md#commit-message-format
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

Other information:

[graingert]

This could break people relying on unhandled rejections never being real exceptions. To be non-breaking we could add a $unhandledRejectionHandler service that takes a rejection, and delegates to $exceptionHandler this way I could add a handler that passes the exception directly but the default would be to strip the error and tasty tracebacks

[gkalpak]

Actually, the "juicy info" does already exist. It is just stringified into a less juicy {} (which we need to fix).
Closing as duplicate of #14631.

[graingert]

@gkalpak stringifying the exception breaks trace-back info because angular doesn't stringify errors properly.

Angular calls Errors 'exceptions' and brutally stringifies them before they can be safely carried to the gentle, sweet, embrace of window.onerror.

[graingert]

@gkalpak no it doesn't.

Nobody wants angular to mess with their Errors and turn them into 'exceptions' for the $exceptionHandler

re-opened for your delectation and delight at #15527

[gkalpak]

That's what I meant by "we need to fix it". Embarrassing as it may be, I have to admit I did not realize this was a PR, until now. I thought it was an issue 😳

Sorry, for not paying attention and thx for your perseverance. I promise I'll treat #15527 rightly 😛