android: Make ChildExitObserver observe CrashHandlerHost

This change causes a CrashHandlerHost to be instantiated, but
ChildExitObserver won't receive child crash signals until
CrashHandlerHost begins monitoring child processes.

Also fixes compilation of crash_handler_host_linux.* on Android by
not compiling breakpad::CrashHandlerHostLinux, which was never used on
Android.

Bug: crashpad:30
Change-Id: I00d1b1b1e0604056a9d64dc070be5aa9638a6d81
Reviewed-on: https://chromium-review.googlesource.com/1150411
Reviewed-by: Mark Mentovai <mark@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Commit-Queue: Joshua Peraza <jperaza@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578081}
4 files changed