When creating a tab contents for a browser in the RVHDelegateHelper, create a wrapper immediately.

chrome/test/data/extensions/api_test/webrequest/framework.js

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 var getURL = chrome.extension.getURL;
 var deepEq = chrome.test.checkDeepEq;
 var expectedEventData;
 var capturedEventData;
 var expectedEventOrder;
 var tabId;
+var tabIdMap;
 var testServerPort;
 var testServer = "www.a.com";
 var eventsCaptured;
 
 function runTests(tests) {
   chrome.tabs.create({url: "about:blank"}, function(tab) {
     tabId = tab.id;
+    tabIdMap = {};
+    tabIdMap[tabId] = 0;
     chrome.test.getConfig(function(config) {
       testServerPort = config.testServer.port;
       chrome.test.runTests(tests);
     });
   });
 }
 
 // Returns an URL from the test server, fixing up the port. Must be called
 // from within a test case passed to runTests.
 function getServerURL(path, opt_host) {
@@ skipping 36 matching lines @@
   eventsCaptured = chrome.test.callbackAdded();
   tabAndFrameUrls = {};  // Maps "{tabId}-{frameId}" to the URL of the frame.
   removeListeners();
   initListeners(filter || {}, extraInfoSpec || []);
   // Fill in default values.
   for (var i = 0; i < expectedEventData.length; ++i) {
     if (!expectedEventData[i].details.method) {
       expectedEventData[i].details.method = "GET";
     }
     if (!expectedEventData[i].details.tabId) {
-      expectedEventData[i].details.tabId = tabId;
+      expectedEventData[i].details.tabId = tabIdMap[tabId];
     }
     if (!expectedEventData[i].details.type) {
       expectedEventData[i].details.type = "main_frame";
     }
   }
 }
 
 function checkExpectations() {
   if (capturedEventData.length < expectedEventData.length) {
     return;
@@ skipping 69 matching lines @@
     chrome.test.assertTrue('tabId' in details &&
                             typeof details.tabId === 'number');
     var key = details.tabId + "-" + details.frameId;
     if (details.type == "main_frame" || details.type == "sub_frame") {
       tabAndFrameUrls[key] = details.url;
     }
     details.frameUrl = tabAndFrameUrls[key] || "unknown frame URL";
   }
   delete details.frameId;
 
+  // This assigns unique IDs to newly opened tabs. However, the new IDs are only
+  // deterministic, if the order in which the tabs are opened is deterministic.
+  if (!(details.tabId in tabIdMap)) {
+    tabIdMap[details.tabId] = Object.keys(tabIdMap).length;
+  }
+  details.tabId = tabIdMap[details.tabId];
+
   delete details.requestId;
   delete details.timeStamp;
   if (details.requestHeaders) {
     details.requestHeadersValid = checkUserAgent(details.requestHeaders);
     delete details.requestHeaders;
   }
   if (details.responseHeaders) {
     details.responseHeadersExist = true;
     delete details.responseHeaders;
   }
@@ skipping 86 matching lines @@
   helper(chrome.experimental.webRequest.onBeforeRequest);
   helper(chrome.experimental.webRequest.onBeforeSendHeaders);
   helper(chrome.experimental.webRequest.onAuthRequired);
   helper(chrome.experimental.webRequest.onSendHeaders);
   helper(chrome.experimental.webRequest.onHeadersReceived);
   helper(chrome.experimental.webRequest.onResponseStarted);
   helper(chrome.experimental.webRequest.onBeforeRedirect);
   helper(chrome.experimental.webRequest.onCompleted);
   helper(chrome.experimental.webRequest.onErrorOccurred);
 }