Add a policy to re-enable deprecated web platform features.

components/policy/resources/policy_templates.json

Index: components/policy/resources/policy_templates.json
diff --git a/components/policy/resources/policy_templates.json b/components/policy/resources/policy_templates.json
index 22b54d4677e5e63d7e87fe3236af96c1d9d7fad2..af60d7062da5cb9338e25ee7cb010302f4c01123 100644
--- a/components/policy/resources/policy_templates.json
+++ b/components/policy/resources/policy_templates.json
@@ -118,7 +118,7 @@
 #   persistent IDs for all fields (but not for groups!) are needed. These are
 #   specified by the 'id' keys of each policy. NEVER CHANGE EXISTING IDs,
 #   because doing so would break the deployed wire format!
-#   For your editing convenience: highest ID currently used: 264
+#   For your editing convenience: highest ID currently used: 265
 #
 # Placeholders:
 #   The following placeholder strings are automatically substituted:
@@ -6365,6 +6365,30 @@
 
       If the policy is left not set, the user can choose an image to be shown on the desktop and on the login screen background.''',
     },
+    {
+      'name': 'EnableDeprecatedWebPlatformFeatures',
+      'type': 'list',
+      'schema': {
+        'type': 'array',
+        'items': { 'type': 'string' },
+      },
+      'supported_on': ['chrome.*:36-', 'chrome_os:36-'],
+      'features': {
+        'dynamic_refresh': True,
+        'per_profile': True,
+      },
+      'example_value': [],
+      'id': 265,
+      'caption': '''Enable deprecated web platform features''',
+      'desc': '''Specify a list of deprecated web platform features to re-enable.
+
+      This policy gives administrators the ability to re-enable deprecated web platform features for a limited time. Features are identified by a string tag and the features corresponding to the tags included in the list specified by this policy will get re-enabled.
+
+      The following tags are currently defined:
+      - ShowModalDialog

[Andrew T Wilson (Slow), 2014/05/08 11:32:45]

Should update this to include an expiration date as we previously discussed

[abarth-chromium, 2014/05/10 00:27:39]

Yeah, I think that's a good idea to make sure admins know how long they've got.

[Mattias Nissler (ping if slow), 2014/05/19 15:03:08]

Done.

+
+      If this policy is left not set or the list is empty, all deprecated web platform features will remain disabled.''',
+    },
   ],
   'messages': {
     # Messages that are not associated to any policies.