toolchain_utils: chrome_src flag for buildbot_test_toolchains

At present, buildbot_test_toolchains always uses the chroot's
chrome checkout for running telemetry tests. This CL allows
callers to change that behaviour with the --chrome_src
flag.

BUG=b:255191595
TEST=./run_tests.py
TEST=Ran on chrotomation with --chrome_src=doesntexist

Change-Id: I7099b13882b72aabf0a4988fec20b90ee80a873f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/4201149
Tested-by: Jordan Abrahams-Whitehead <ajordanr@google.com>
Reviewed-by: George Burgess <gbiv@chromium.org>
Commit-Queue: Jordan Abrahams-Whitehead <ajordanr@google.com>
1 file changed