Don't write pyc files if running from Cog

Many tools use vpython so we can avoid pyc writes by
disabling them at this layer.

Bug: b/320565954
Change-Id: I50cd04968810ecc186d5abe6c67e54ae1647c739
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5812665
Commit-Queue: Erik Staab <estaab@chromium.org>
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>

vpython3

@@ -37,6 +37,11 @@ fi
 export DEPOT_TOOLS_DIR="${DEPOT_TOOLS_DIR:-$(dirname "$0")}"
 export DEPOT_TOOLS_UNAME_S="${DEPOT_TOOLS_UNAME_S:-$(uname -s | tr '[:upper:]' '[:lower:]')}"
 
+# Don't write pyc files if running from a Cog workspace.
+if [[ "$(pwd)" == "/google/cog/"* ]]; then
+  export PYTHONDONTWRITEBYTECODE=1
+fi
+
 source "${DEPOT_TOOLS_DIR}/cipd_bin_setup.sh"
 CIPD_ROOT=$(cipd_bin_setup) &> /dev/null