Exclude immersive-mode controller tests from non-chromeos in gyp.

Instead of having the entire file in #if defined(OS_CHROME), simply exclude
the file in .gyp.

BUG=none
R=jamescook@chromium.org

Review URL: https://codereview.chromium.org/148003002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247294 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247294