[DevTools] Move extension embedder message to InspectorFrontentAPI.

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.extensionServer._overridePlatformExtensionAPIForTest = function(extensionInfo)
+WebInspector.extensionServer._overridePlatformExtensionAPIForTest = function(extensionInfo, inspectedTabId)
 {
     WebInspector.extensionServer._registerHandler("evaluateForTestInFrontEnd", onEvaluate);
 
     function platformExtensionAPI(coreAPI)
     {
         window.webInspector = coreAPI;
         window._extensionServerForTests = extensionServer;
     }
     return platformExtensionAPI.toString();
 }
@@ skipping 28 matching lines @@
 InspectorTest.runExtensionTests = function()
 {
     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 }]);
+        InspectorFrontendAPI.addExtensions([{ startPage: extensionURL, name: "test extension", exposeWebInspectorNamespace: true }]);
         WebInspector.extensionServer.initializeExtensions();
     });
 }
 
 }
 
 function extension_showPanel(panelId, callback)
 {
     evaluateOnFrontend("InspectorTest.showPanel(unescape('" + escape(panelId) + "')).then(function() { reply(); });", callback);
 }
 
 var test = function()
 {
     InspectorTest.runExtensionTests();
 }