Don't overwrite toolchains if they were downloaded manually
Don't overwrite toolchains if they were downloaded manually

Apparently r7299 introduced change which broke manual override
mode.  People rarely notice that because scripts are rarely
updated but it's still an error.

TEST=create manual override toolchain, touch download_utils.py then run sync
R=bradnelson@google.com

Review URL: https://codereview.chromium.org/47923019

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@12355 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client