In the interest of being more certain about the imminent fatal fate of crashing processes, we shouldn't restore crash signal handlers after dumping child processes.

Crashpad does restore browser crash signal handlers so that apps using WebView can use their own signal handlers, but this shouldn't be necessary for child processes.

Currently some tests depend on the tombstone producing signal handler installed by Bionic. Perhaps they can be updated to use minidumps produced by Crashpad instead?

https://bugs.chromium.org/p/chromium/issues/detail?id=911678
https://bugs.chromium.org/p/chromium/issues/detail?id=912166
https://bugs.chromium.org/p/chromium/issues/detail?id=912161