Make it possible to have multiple InspectorBackends

sky/framework/inspector/inspector.sky

 <import src="/mojo/public/sky/connection.sky" as="connection" />
 <import src="/mojo/public/sky/core.sky" as="core" />
 <import src="/mojo/public/sky/support.sky" as="support" />
 <import src="/sky/services/inspector/inspector.mojom.sky" as="inspector" />
 <import src="console-agent.sky" as="ConsoleAgent" />
 <import src="dom-agent.sky" as="DOMAgent" />
 <import src="page-agent.sky" as="PageAgent" />
 <import src="worker-agent.sky" as="WorkerAgent" />
 <import src="runtime-agent.sky" as="RuntimeAgent" />
 <import src="indexeddb-agent.sky" as="IndexedDBAgent" />
@@ skipping 75 matching lines @@
 };
 
 var frontendHandle = internals.connectToService(
     "mojo:sky_inspector_server", inspector.InspectorFrontend.name);
 window.frontendConnection = new connection.Connection(
     frontendHandle,
     InspectorBackend,
     inspector.InspectorFrontend.proxyClass);
 
 window.frontend = frontendConnection.remote;
-frontend.listen(9898);
 </script>