Use main branch as the default branch

R=apolito@google.com

Change-Id: I6a2ed557b9e8d45194b2fe4ea5327ce62020733c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3000134
Reviewed-by: Anthony Polito <apolito@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
diff --git a/gclient_scm.py b/gclient_scm.py
index dc406d5..661bb50 100644
--- a/gclient_scm.py
+++ b/gclient_scm.py
@@ -252,7 +252,7 @@
   def diff(self, options, _args, _file_list):
     _, revision = gclient_utils.SplitUrlRevision(self.url)
     if not revision:
-      revision = 'refs/remotes/%s/master' % self.remote
+      revision = 'refs/remotes/%s/main' % self.remote
     self._Run(['-c', 'core.quotePath=false', 'diff', revision], options)
 
   def pack(self, _options, _args, _file_list):
@@ -866,7 +866,7 @@
       # Don't reuse the args.
       return self.update(options, [], file_list)
 
-    default_rev = "refs/heads/master"
+    default_rev = "refs/heads/main"
     if options.upstream:
       if self._GetCurrentBranch():
         upstream_branch = scm.GIT.GetUpstreamBranch(self.checkout_path)