Add a chromium version to policy template files.

grit/format/policy_templates/writers/json_writer.py

Index: grit/format/policy_templates/writers/json_writer.py
===================================================================
--- grit/format/policy_templates/writers/json_writer.py	(revision 177)
+++ grit/format/policy_templates/writers/json_writer.py	(working copy)
@@ -39,6 +39,9 @@
   def PreprocessPolicies(self, policy_list):
     return self.FlattenGroupsAndSortPolicies(policy_list)
 
+  def WriteComment(self, comment):
+    self._out.append('// ' + comment)
+
   def WritePolicy(self, policy):
     if policy['type'] == 'external':
       # This type can only be set through cloud policy.
@@ -69,6 +72,9 @@
     self._first_written = False
 
   def BeginTemplate(self):
+    if self._GetChromiumVersionString() is not None:
+      self.WriteComment(self.config['build'] + ''' version: ''' + \
+          self._GetChromiumVersionString())
     self._out.append(TEMPLATE_HEADER)
 
   def EndTemplate(self):