Defer media loading while on cellular networks.

third_party/WebKit/LayoutTests/netinfo/resources/netinfo_common.js

 window.jsTestIsAsync = true;
 
 var connection = navigator.connection;
 var initialType = "bluetooth";
 var initialDownlinkMax = 1.0;
 var newConnectionType = "ethernet";
 var newDownlinkMax = 2.0;
 
 // Suppress connection messages information from the host.
 if (window.internals) {
     internals.setNetworkStateNotifierTestOnly(true);
     internals.setNetworkConnectionInfo(initialType, initialDownlinkMax);
+
+    // Reset the state of the singleton network state notifier.
+    window.addEventListener('beforeunload', function() {
+        internals.setNetworkStateNotifierTestOnly(false);
+    }, false);
 }