Add git thaw/freeze to depot_tools.

git_freezer.py

Index: git_freezer.py
diff --git a/git_freezer.py b/git_freezer.py
new file mode 100755
index 0000000000000000000000000000000000000000..6e28b3e342b066f582fd46c48153f90a8038ebf9
--- /dev/null
+++ b/git_freezer.py
@@ -0,0 +1,73 @@
+#!/usr/local/bin/python
+import sys
+import re
+import optparse
+
+import subcommand
+import subprocess2
+
+from git_common import run, stream
+
+FREEZE = 'FREEZE'
+SECTIONS = {
+  'indexed': 'soft',
+  'unindexed': 'mixed'
+}
+MATCHER = re.compile(r'%s.(%s)' % (FREEZE, '|'.join(SECTIONS)))
+
+
+def freeze():
+  took_action = False
+
+  try:
+    run('commit', '-m', FREEZE + '.indexed')
+    took_action = True
+  except subprocess2.CalledProcessError:
+    pass
+
+  try:
+    run('add', '-A')
+    run('commit', '-m', FREEZE + '.unindexed')
+    took_action = True
+  except subprocess2.CalledProcessError:
+    pass
+
+  if not took_action:
+    return 'Nothing to freeze.'
+
+
+def thaw():
+  took_action = False
+  for sha in (s.strip() for s in stream('rev-list', 'HEAD').xreadlines()):
+    msg = run('show', '--format=%f%b', '-s', 'HEAD')
+    match = MATCHER.match(msg)
+    if not match:
+      if not took_action:
+        return 'Nothing to thaw.'
+      break
+
+    run('reset', '--' + SECTIONS[match.group(1)], sha)
+    took_action = True
+
+
+def CMDfreeze(parser, args):  # pragma: no cover
+  """Freeze a branch's changes."""
+  parser.parse_args(args)
+  return freeze()
+
+
+def CMDthaw(parser, args):  # pragma: no cover
+  """Returns a frozen branch to the state before it was frozen."""
+  parser.parse_args(args)
+  return thaw()
+
+
+def main():  # pragma: no cover
+  dispatcher = subcommand.CommandDispatcher(__name__)
+  ret = dispatcher.execute(optparse.OptionParser(), sys.argv[1:])
+  if ret:
+    print ret
+
+
+if __name__ == '__main__':  # pragma: no cover
+  main()