Convert the inspector framework to use ES6 classes.

sky/framework/inspector/console-agent.sky

 <script>
-function ConsoleAgent() {
+class ConsoleAgent {
+  constructor() {
+    Object.preventExtensions(this);
+  }
+
+  enable() {
+    return {
+      result: true,
+    };
+  }
 }
 
-ConsoleAgent.prototype.enable = function() {
-  return {
-    result: true,
-  };
-};
-
 module.exports = ConsoleAgent;
 </script>