Update references to Mac- and Win-specific icon files in official build.

In the internal repository, several Mac- and Windows-specific icon files
have been moved into 'mac' and 'win' subdirectories in
chrome/app/theme/google_chrome. This updates the references to those
icons to refer to their new location.

BUG=333751

Review URL: https://codereview.chromium.org/138553005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246020 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246020