wm: Send SIGABRT on failed asserts.
wm: Send SIGABRT on failed asserts.

We don't get minidumps from Breakpad otherwise.

Review URL: http://codereview.chromium.org/516022

joshfire/chromiumos-platform-window_manager,joshfire/chromiumos-platform-window_manager,joshfire/chromiumos-platform-window_manager,joshfire/chromiumos-platform-window_manager