DevTools: Introduce Target class which holds connection & models

Source/devtools/front_end/InspectorBackend.js

Index: Source/devtools/front_end/InspectorBackend.js
diff --git a/Source/devtools/front_end/InspectorBackend.js b/Source/devtools/front_end/InspectorBackend.js
index e8c948d194365b56897d70fd8c093da3e3ec2b88..bd1cc72f64bcac9c71473d48b04a1c2898131d2d 100644
--- a/Source/devtools/front_end/InspectorBackend.js
+++ b/Source/devtools/front_end/InspectorBackend.js
@@ -338,6 +338,14 @@ InspectorBackendClass.Connection.prototype = {
     },
 
     /**
+     * @return {!Array.<string>}
+     */
+    domains: function()
+    {
+        return Object.keys(this._agents);
+    },
+
+    /**
      * @param {string} domain
      * @param {string} method
      * @param {?Object} params