We treat these exceptions the same way we treat fatal errors: report
the error message to our server and then allow the exception to reach
the top level.
We could also override document.onerror, but don't. There are a
couple of ramifications of this:
* Exceptions caused by event handlers directly attached to DOM
elements aren't handled
* Exceptions caused by code at the top level that triggers an error
(such as parse errors in our Javascript files) aren't handled
The reason we don't override document.onerror is because the
document.onerror handler has a limited interface and doesn't receive
the exception object. It only gets the message, file, and line
number of the error. Additionally, exceptions that we allow to
propogate out of blueslip trigger an onerror event when they're never
caught. In order to avoid handling the error twice (once by blueslip
and once by the onerror handler), we'd have to encode the fact that
the error has already been handled in the error message, which is
pretty ugly.
(imported from commit 7f049ae519dc198a9f7cfd41fd5dd18e584bd061)
This is to let us pass in the stack trace of an existing exception,
which will be required in a upcoming commit.
(imported from commit 421366a7a01deb770b7620417fb4660769c5db53)
The new system, called blueslip, makes errors fatal when in debug
mode and only output a message when running in production. In the
future, it could also send user errors back to us automatically.
(imported from commit 1232607c0311e885c8b5a5e8a45ffb28822426e0)
