Added transient 502 errors to 'git_retry' list.
Added transient 502 errors to 'git_retry' list.

BUG=chromium:430343
TEST=None

Review URL: https://codereview.chromium.org/701843004

git-svn-id: bd64dd6fa6f3f0ed0c0666d1018379882b742947@292868 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

svn2github/chromium-depot-tools,svn2github/chromium-depot-tools,svn2github/chromium-depot-tools