GitLab

It is more traditional (and recommended) to have GN targets closer to the source
files it builds.

BUG=432959
TEST=gn gen out-gn && ninja -C out-gn compositor_model_bench
R=sievers@chromium.org, dpranke@chromium.org

Review URL: https://codereview.chromium.org/1032193002

Cr-Commit-Position: refs/heads/master@{#322226}