Increase URLRequestTest CloseBrowser timeout to reduce flakes (fixes issue #2756)

Tests for incomplete request behavior use a timeout to trigger CloseBrowser
and terminate the test case. Recent architectural changes in Chromium have
likely increased the minimum delay required to spin up a working browser
instance and initiate the request. Consequently we need to wait longer before
closing the browser.

To test:
Run `ceftests --gtest_filter=URLRequestTest.*Incomplete* --gtest_repeat=5`.
All test runs should succeed.

tests/ceftests/urlrequest_unittest.cc

@@ -2836,7 +2836,7 @@ class RequestTestHandler : public TestHandler {
     SetSignalCompletionWhenAllBrowsersClose(false);
     CefPostDelayedTask(
         TID_UI, base::Bind(&TestHandler::CloseBrowser, GetBrowser(), false),
-        100);
+        1000);
   }
 
   // Test run is complete. It ran in either the browser or render process.