Swarming: Ensure depot_tools is in PATH when compiling

Turns out we were "lucky" for our Linux bots which already have depot_tools in PATH. The Mac bot does have depot_tools, but it's not in PATH.  Add it in the script to ensure we can always get to it.

NOTRY=true
BUG=skia:4763
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1823653002

Review URL: https://codereview.chromium.org/1823653002
1 file changed