Consider an immediate redirect as machine-initiated and slow one as...

chrome/test/data/History/history_length_test_page_2.html

Index: chrome/test/data/History/history_length_test_page_2.html
===================================================================
--- chrome/test/data/History/history_length_test_page_2.html	(revision 17847)
+++ chrome/test/data/History/history_length_test_page_2.html	(working copy)
@@ -18,14 +18,15 @@
               "Page 2 must not be visited in navigating backward/forward");
     return false;
   }
-  setTimeout(OnInitialLoad, 100);
+  setTimeout(OnInitialLoad, 50);
   return true;
 }
 
 function OnInitialLoad() {
   if (window.history.length != 3) {
     onFailure("History_Length_Test_2", 1,
-              "History length mismatch on initial load at page 2");
+              "History length mismatch on initial load at page 2: " +
+              window.history.length);
     return false;
   }
   // Redirect to page 3.