Fix git checkout.
Fix git checkout.

Previously only the git_setup and submodule update steps would respect build_dir,
which basically just screwed everything up.

R=joshualitt@chromium.org, stip@chromium.org
BUG=

Review URL: https://codereview.chromium.org/69843002

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@234556 0039d316-1c4b-4281-b951-d872f2087c98

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