Attempt to fix hanging WebRequestBlocking.

chrome/test/data/extensions/api_test/webrequest/test_blocking.html

 <script src="framework.js">
 </script>
 <script>
+var pass = chrome.test.callbackPass;
+
 // Constants as functions, not to be called until after runTests.
 function getURLEchoUserAgent() {
   return getServerURL('echoheader?User-Agent');
 }
 
 runTests([
   // Navigates to a page with subresources, with a blocking handler that
   // cancels the page request. The page will not load, and we should not
   // see the subresources.
   function complexLoadCancelled() {
     expect(
       [  // events
         { label: "onBeforeRequest",
           event: "onBeforeRequest",
           details: {
             method: "GET",
             tabId: tabId,
             type: "main_frame",
-            url: getURL("complexLoad/a.html"),
-            frameUrl: getURL("complexLoad/a.html")
+            url: getURL("complexLoad/b.html"),
+            frameUrl: getURL("complexLoad/b.html")
           },
           retval: {cancel: true}
         },
         // Cancelling is considered an error.
         { label: "onErrorOccurred",
           event: "onErrorOccurred",
           details: {
-            url: getURL("complexLoad/a.html"),
+            url: getURL("complexLoad/b.html"),
             fromCache: false,
             error: "net::ERR_EMPTY_RESPONSE"
             // Request to chrome-extension:// url has no IP.
           }
         },
       ],
       [  // event order
         ["onBeforeRequest", "onErrorOccurred"]
       ],
       {},  // filter
       ["blocking"]);
-    console.log("load canc: navigating to a");
-    navigateAndWait(getURL("complexLoad/a.html"));
+    console.log("load canc: navigating to b");
+    navigateAndWait(getURL("complexLoad/b.html"), function() {
+      // Workaround for hanging test. For some reason, if we try to load
+      // a new URL in the current tab, it hangs on the buildbot.
+      // See http://crbug.com/91715
+      chrome.tabs.create({url: "about:blank"}, pass(function(tab) {
+        tabId = tab.id;
+      }));
+    });
   },
 
   // Navigates to a page with a blocking handler that redirects to a different
   // page.
   // TODO(mpcomplete): We should see an onBeforeRedirect as well, but our
   // process switching logic cancels the original redirect request and
   // starts a new one instead. See http://crbug.com/79520.
   function complexLoadRedirected() {
     expect(
       [  // events
@@ skipping 121 matching lines @@
       console.log("mod headers: 3");
       chrome.tabs.executeScript(tabId,
         {
           code: "chrome.extension.sendRequest(" +
               "{pass: document.body.innerText.indexOf('FoobarUA') >= 0});"
         });
     });
   },
 ]);
 </script>