DevTools: introduce multitarget model listeners

LayoutTests/http/tests/inspector/inspector-test.js

Index: LayoutTests/http/tests/inspector/inspector-test.js
diff --git a/LayoutTests/http/tests/inspector/inspector-test.js b/LayoutTests/http/tests/inspector/inspector-test.js
index ba26fe61f5c77ea60cfdca6c171c8b49232ae011..f0ff1951b9f643ff92e014b80ed64ebeddbc0da8 100644
--- a/LayoutTests/http/tests/inspector/inspector-test.js
+++ b/LayoutTests/http/tests/inspector/inspector-test.js
@@ -614,6 +614,8 @@ WebInspector.targetManager.observeTargets({
             WebInspector.domModel = target.domModel;
         if (!WebInspector.consoleModel)
             WebInspector.consoleModel = target.consoleModel;
+        if (!WebInspector.networkManager)
+            WebInspector.networkManager = target.networkManager;
     },
 
     targetRemoved: function(target) { }