CrOS: Update Chromite pinning.
CrOS: Update Chromite pinning.

Update Chromite pinning to afdd4374a659627b43658b4747dea2eb5ab8e1fc
to pick up: https://chromium-review.googlesource.com/#/c/250862/

TBR=petermayo@chromium.org
BUG=chromium:415785
TEST=None

Review URL: https://codereview.chromium.org/974743002

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@294296 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build