CrOS: Update Chromite pin.
CrOS: Update Chromite pin.

Update Chromite pin to:
785cb2b424efc25cbcfc7064929342f663f24386

TBR=petermayo@chromium.org
BUG=None
TEST=presubmit

Review URL: https://codereview.chromium.org/1004593006

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@294539 0039d316-1c4b-4281-b951-d872f2087c98

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