Move control of updating toolchain into src/

Moved out of depot_tools here: https://codereview.chromium.org/168603004/

The control is in src/ now, but logic for de-duplication is still in depot_tools.

This changes the default, so that VS2013 will be the default toolchain.

R=iannucci@chromium.org
BUG=323300,309197

Review URL: https://codereview.chromium.org/175573004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252733 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252733