Add gerrit Change-Id to commit messages if they do not have one.

gclient.py

Index: gclient.py
diff --git a/gclient.py b/gclient.py
index ab52cc8eee6098eed83c4ce41dd652606ebf4bea..c78ae87bc39c504f541e09696fb389b3f04676db 100644
--- a/gclient.py
+++ b/gclient.py
@@ -455,6 +455,11 @@ class Dependency(gclient_utils.WorkItem, DependencySettings):
       self.recursion_override = local_scope.get('recursion')
       logging.warning(
           'Setting %s recursion to %d.', self.name, self.recursion_limit)
+    # Check if 'target_os' is present in the DEPS file. If yes, then add OSes
+    # specified to the set of enforced OSes.
+    if 'target_os' in local_scope:
+      self.root._enforced_os = tuple(
+          set(local_scope['target_os']).union(self.root._enforced_os))
     # load os specific dependencies if defined.  these dependencies may
     # override or extend the values defined by the 'deps' member.
     if 'deps_os' in local_scope: