Use closest git commit to the target svn revision.
Otherwise --checkout may be required to create
a git commit for a specific svn revision.

NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/11886086

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@179023 0039d316-1c4b-4281-b951-d872f2087c98