Roll Skia DEPS to r12560

This DEPS roll just bumps from Skia r12555 to r12560.

R=reed@google.com

Review URL: https://codereview.chromium.org/110253002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239486 0039d316-1c4b-4281-b951-d872f2087c98
Update .DEPS.git

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239487 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239487