Only force preload=none over cellular for http, https, ftp URLs.

third_party/WebKit/LayoutTests/media/video-preload-cellular-test.js

-function cellular_preload_test() {
-  async_test(function(t) {
-    internals.setNetworkStateNotifierTestOnly(true);
-    internals.setNetworkConnectionInfo('cellular', 2.0);
-
-    var video = document.querySelector('video');
-    assert_equals(video.preload, 'none')
-    video.src = 'resources/test-positive-start-time.webm';
-
-    video.onsuspend = t.step_func_done();
-    video.onprogress = t.unreached_func();
-    t.add_cleanup(function() {
-      internals.setNetworkStateNotifierTestOnly(false);
-    });
-  });
-}