gclient runhooks on env updates on goma canary Windows.
gclient runhooks on env updates on goma canary Windows.

Revival of https://codereview.chromium.org/1027123002/.
Changes from the previous:
- only affects goma canary bots.
- use chromium_utils.GetGClientCommand() instead of directly using 'gclient'.

Review URL: https://codereview.chromium.org/1032273002

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@294586 0039d316-1c4b-4281-b951-d872f2087c98

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