Prevent git from using any external diff program that may have been

configured for it when figuring out the patch to upload to the try
server.  This prevents git installations where the diff is configured
to use an interactive tool to work without doing nasty workarounds.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/1958002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@47661 0039d316-1c4b-4281-b951-d872f2087c98

scm.py

@@ -277,7 +277,8 @@ class GIT(object):
     files, usually in the prospect to apply the patch for a try job."""
     if not branch:
       branch = GIT.GetUpstreamBranch(cwd)
-    command = ['diff', '-p', '--no-prefix', branch + "..." + branch_head]
+    command = ['diff', '-p', '--no-prefix', '--no-ext-diff',
+               branch + "..." + branch_head]
     if not full_move:
       command.append('-C')
     # TODO(maruel): --binary support.