Every time I write a json file, I end up wishing I put my toplevel items
into non-toplevel items down the line when I want to add more stuff to the
json file.  Address this now, while no toolchain with this json file has
been built yet.

Follow-up to https://codereview.chromium.org/1706423002/

BUG=495204

Review URL: https://codereview.chromium.org/1718083003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@298908 0039d316-1c4b-4281-b951-d872f2087c98