Bug 622315: Refuse to navigate if a navigation is already pending. r=bz

docshell/shistory/src/nsSHistory.cpp

@@ -716,7 +716,13 @@ nsSHistory::GetCanGoBack(PRBool * aCanGoBack)
   NS_ENSURE_ARG_POINTER(aCanGoBack);
   *aCanGoBack = PR_FALSE;
 
+  // If there is already a pending navigation, we cannot go back.
   PRInt32 index = -1;
+  NS_ENSURE_SUCCESS(GetRequestedIndex(&index), NS_ERROR_FAILURE);
+
+  if(index != -1)
+    return NS_OK;
+
   NS_ENSURE_SUCCESS(GetIndex(&index), NS_ERROR_FAILURE);
   if(index > 0)
      *aCanGoBack = PR_TRUE;
@@ -730,9 +736,15 @@ nsSHistory::GetCanGoForward(PRBool * aCanGoForward)
   NS_ENSURE_ARG_POINTER(aCanGoForward);
   *aCanGoForward = PR_FALSE;
 
+  // If there is already a pending navigation, we cannot go forward.
   PRInt32 index = -1;
   PRInt32 count = -1;
 
+  NS_ENSURE_SUCCESS(GetRequestedIndex(&index), NS_ERROR_FAILURE);
+
+  if(index != -1)
+    return NS_OK;
+
   NS_ENSURE_SUCCESS(GetIndex(&index), NS_ERROR_FAILURE);
   NS_ENSURE_SUCCESS(GetCount(&count), NS_ERROR_FAILURE);