Add first chance exception handler API

This change adds the option for Breakpad hosts to register a callback
that gets the first chance to handle an exception. The handler will 
return true if it handled the exception and false otherwise.

The primary use case is V8's trap-based bounds checking support for
WebAssembly.

Bug:
Change-Id: I5aa5b87d1229f1cef905a00404fa2027ee86be56
Reviewed-on: https://chromium-review.googlesource.com/509994
Reviewed-by: Mark Mentovai <mark@chromium.org>

Cr-Mirrored-From: https://chromium.googlesource.com/breakpad/breakpad
Cr-Mirrored-Commit: 1628d99f7b21b6920ac8bf197b2acd38021f1df9
3 files changed