GitLab

The child process launcher now switches to the host executable's
path before running a new child process. That breaks mash_runner
code which launches the host executable if the host executable was
invoked by relative path.

This changes mash_runner to always reference the host executable
by absolute path when rewriting child command lines.

BUG=None
R=sky@chromium.org

Review-Url: https://codereview.chromium.org/2573593002
Cr-Commit-Position: refs/heads/master@{#437961}