Add --ignore-history to merge command (only applicable to branch merges).

drover.py

 # Copyright (c) 2009 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.
 
 import optparse
 import os
 import re
 import subprocess
 import sys
 import webbrowser
@@ skipping 154 matching lines @@
     os.system(command)
 
 def mergeRevision(url, revision):
   paths = getBestMergePaths(url, revision)
   export_map = getBestExportPathsMap(url, revision)
 
   for path in paths:
     if export_map.has_key(path):
       continue
     command = ('svn merge -N -r ' + str(revision-1) + ":" + str(revision) + " ")
-    command = command + url + path + "@" + str(revision) + " ." + path
+    command += " --ignore-ancestry "
+    command += url + path + "@" + str(revision) + " ." + path
 
     print command
     os.system(command)
 
 def exportRevision(url, revision):
   paths = getBestExportPathsMap(url, revision).keys()
   paths.sort()
 
   for path in paths:
     command = ('svn export -N ' + url + path + "@" + str(revision) + " ."  +
@@ skipping 277 matching lines @@
 
   if not options.merge and not options.revert:
     option_parser.error("You need at least --merge or --revert")
     sys.exit(1)
 
   if options.merge and not options.branch:
     option_parser.error("--merge requires a --branch")
     sys.exit(1)
 
   sys.exit(main(options, args))