Revert of Revert "Add (another) argument to break git locks in gclient."

gclient_scm.py

Index: gclient_scm.py
diff --git a/gclient_scm.py b/gclient_scm.py
index 1aeb69dbf7556b2596f15949f775159aa8e30fba..9a6f5123419cef246e638dc28ae3caf0679cd4ee 100644
--- a/gclient_scm.py
+++ b/gclient_scm.py
@@ -326,6 +326,27 @@
         if os.path.exists(disabled_hook_path):
           os.remove(disabled_hook_path)
         os.rename(os.path.join(hook_dir, f), disabled_hook_path)
+
+  def _maybe_break_locks(self, options):
+    """This removes all .lock files from this repo's .git directory, if the
+    user passed the --break_repo_locks command line flag.
+
+    In particular, this will cleanup index.lock files, as well as ref lock
+    files.
+    """
+    if options.break_repo_locks:
+      git_dir = os.path.join(self.checkout_path, '.git')
+      for path, _, filenames in os.walk(git_dir):
+        for filename in filenames:
+          if filename.endswith('.lock'):
+            to_break = os.path.join(path, filename)
+            self.Print('breaking lock: %s' % (to_break,))
+            try:
+              os.remove(to_break)
+            except OSError as ex:
+              self.Print('FAILED to break lock: %s: %s' % (to_break, ex))
+              raise
+
 
   def update(self, options, args, file_list):
     """Runs git to update or transparently checkout the working copy.
@@ -432,6 +453,8 @@
       self._UpdateBranchHeads(options, fetch=False)
       self.Print('________ unmanaged solution; skipping %s' % self.relpath)
       return self._Capture(['rev-parse', '--verify', 'HEAD'])
+
+    self._maybe_break_locks(options)
 
     if mirror:
       self._UpdateMirror(mirror, options)