Defer media loading while on cellular networks.

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);
+    });
+  });
+}