DevTools: make extension server a part of core, panels' code should depend on it.

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

 function extensionFunctions()
 {
     var functions = "";
 
     for (symbol in window) {
         if (/^extension_/.exec(symbol) && typeof window[symbol] === "function")
             functions += window[symbol].toString();
     }
     return functions;
 }
 
 var initialize_ExtensionsTest = function()
 {
 
-WebInspector.extensionServerProxy._overridePlatformExtensionAPIForTest = function(extensionInfo)
+WebInspector.extensionServer._overridePlatformExtensionAPIForTest = function(extensionInfo)
 {
-    WebInspector.extensionServerProxy._extensionServer._registerHandler("evaluateForTestInFrontEnd", onEvaluate);
+    WebInspector.extensionServer._registerHandler("evaluateForTestInFrontEnd", onEvaluate);
 
     function platformExtensionAPI(coreAPI)
     {
         window.webInspector = coreAPI;
         window._extensionServerForTests = extensionServer;
     }
     return platformExtensionAPI.toString();
 }
 
 InspectorTest._replyToExtension = function(requestId, port)
 {
     WebInspector.extensionServer._dispatchCallback(requestId, port);
 }
 
 function onEvaluate(message, port)
 {
     function reply(param)
     {
-        WebInspector.extensionServerProxy._extensionServer._dispatchCallback(message.requestId, port, param);
+        WebInspector.extensionServer._dispatchCallback(message.requestId, port, param);
     }
 
     try {
         eval(message.expression);
     } catch (e) {
         InspectorTest.addResult("Exception while running: " + message.expression + "\n" + (e.stack || e));
         InspectorTest.completeTest();
     }
 }
 
 InspectorTest.showPanel = function(panelId)
 {
     if (panelId === "extension")
         panelId = WebInspector.inspectorView._tabbedPane._tabs[WebInspector.inspectorView._tabbedPane._tabs.length - 1].id;
     return WebInspector.inspectorView.showPanel(panelId);
 }
 
 InspectorTest.runExtensionTests = function()
 {
-    WebInspector.extensionServerProxy.setFrontendReady();
     RuntimeAgent.evaluate("location.href", "console", false, function(error, result) {
         if (error)
             return;
         var pageURL = result.value;
         var extensionURL = (/^https?:/.test(pageURL) ?
             pageURL.replace(/^(https?:\/\/[^/]*\/).*$/,"$1") :
             pageURL.replace(/\/inspector\/extensions\/[^/]*$/, "/http/tests")) +
             "/inspector/resources/extension-main.html";
         WebInspector.addExtensions([{ startPage: extensionURL, name: "test extension", exposeWebInspectorNamespace: true }]);
     });
 }
 
 }
 
 function extension_showPanel(panelId, callback)
 {
     evaluateOnFrontend("InspectorTest.showPanel(unescape('" + escape(panelId) + "')).then(function() { reply(); });", callback);
 }
 
 var test = function()
 {
     InspectorTest.runExtensionTests();
 }