Dart: Rename mojo:X -> dart:mojo.X

sky/tests/services/iframe-embed-vmc.sky

 <sky>
 
 <iframe></iframe>
 
 <script>
 import 'dart:async';
 import 'dart:sky';
 import 'dart:sky.internals' as internals;
 import 'dart:typed_data';
 import '/mojo/public/dart/application.dart';
-import 'mojo:bindings';
-import 'mojo:core';
+import 'dart:mojo.bindings';
+import 'dart:mojo.core';
 
 import 'package:mojo/public/interfaces/application/shell.mojom.dart' as shell_mojom;
 import 'package:mojo/services/input_events/public/interfaces/input_events.mojom.dart' as input_events;
 import 'package:mojo/services/view_manager/public/interfaces/view_manager.mojom.dart' as view_manager;
 import 'package:services/js/test/echo_service.mojom.dart' as echo_service_mojom;
 
 class IFrameEmbed extends Application {
   IFrameEmbed.fromHandle(MojoHandle handle) : super.fromHandle(handle);
   IFrameEmbed(MojoMessagePipeEndpoint endpoint) : super(endpoint);
 
@@ skipping 23 matching lines @@
 
 main() {
   var messagePipe = new MojoMessagePipe();
   var app = new IFrameEmbed(messagePipe.endpoints[1]);
   var shellProxy = new shell_mojom.ShellProxy.fromHandle(
       new MojoHandle(internals.takeShellProxyHandle()));
   app.initializeFromShellProxy(shellProxy, [], "");
 }
 </script>
 </sky>