Add optional mandatory policy setting for template generation

grit/format/policy_templates/writer_configuration.py

Index: grit/format/policy_templates/writer_configuration.py
===================================================================
--- grit/format/policy_templates/writer_configuration.py	(revision 175)
+++ grit/format/policy_templates/writer_configuration.py	(working copy)
@@ -33,6 +33,7 @@
       'win_recommended_category_path': ['chromium_recommended'],
       'admx_namespace': 'Chromium.Policies.Chromium',
       'admx_prefix': 'chromium',
+      'linux_policy_path': '/etc/chromium/policies/',
     }
   elif '_google_chrome' in defines:
     config = {
@@ -47,6 +48,7 @@
       'win_recommended_category_path': ['google', 'googlechrome_recommended'],
       'admx_namespace': 'Google.Policies.Chrome',
       'admx_prefix': 'chrome',
+      'linux_policy_path': '/etc/opt/chrome/policies/',
     }
   else:
     raise Exception('Unknown build')