[Mac] Re-add the NSColor sandbox warmup.

It was removed at r254175. While this is not needed in renderer processes, it is
needed for ppapi processes, specifically Flash.

BUG=348304,306348
TBR=avi@chromium.org

Review URL: https://codereview.chromium.org/181063009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254380 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254380