As noticed in the TODO, raw_input (used by ask_for_data) works badly
on background threads. On my Windows it doesn't even print the prompt which
makes it hard to interact with it.

Better to just abort and tell the user of gclient how to proceed.

BUG=

Review URL: https://chromiumcodereview.appspot.com/15421005

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@201295 0039d316-1c4b-4281-b951-d872f2087c98