Add new termination status for failed child process launch.

Treat renderer startup failure as a renderer crash for metrics.

This makes situations where sandbox failures are happening en-masse
without crash reports being produced easier to spot on the stability
dashboard.

BUG=526198,467920

Review URL: https://codereview.chromium.org/1320153002

Cr-Commit-Position: refs/heads/master@{#347060}
17 files changed