grit: policy: sort policy_definitions output for stability

The policy logic sorts a bunch of its keys already to keep the output
stable, especially for unittests.  The policy_definitions section is
not currently sorted which leads to unittest failures on Python 3 as
it happens to iterate differently.  Sort the keys to fix it.

Bug: 983071
Test: `./grit/test_suite_all.py` passes
Change-Id: Iacd30d0edc2a597ada265b4b69664a8d19d9629c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1755389Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#687406}

tools/grit/grit/format/policy_templates_json_unittest.py

@@ -151,13 +151,10 @@ class PolicyTemplatesJsonUnittest(unittest.TestCase):
   "policy_definitions": [
     {
       "caption": "%s",
-      "features": {"can_be_recommended": true, "dynamic_refresh": true},
-      "name": "MainPolicy",
-      "tags": [],
       "desc": "Th\xefP\xefs p\xf4P\xf4l\xefP\xefc\xfdP\xfd d\xf4\xe9P\xf4\xe9s st\xfcP\xfcff.",
-      "type": "main",
       "example_value": true,
-      "supported_on": ["chrome_os:29-"],
+      "features": {"can_be_recommended": true, "dynamic_refresh": true},
+      "name": "MainPolicy",
       "schema": {
         "properties": {
           "default_launch_container": {
@@ -173,7 +170,10 @@ class PolicyTemplatesJsonUnittest(unittest.TestCase):
           }
         },
         "type": "object"
-      }
+      },
+      "supported_on": ["chrome_os:29-"],
+      "tags": [],
+      "type": "main"
     }
   ],
   "policy_atomic_group_definitions": [

tools/grit/grit/gather/policy_json.py

@@ -242,7 +242,7 @@ class PolicyJson(skeleton_gatherer.SkeletonGatherer):
     '''
     for item_count, (item1) in enumerate(items, 1):
       self._AddIndentedNontranslateableChunk(depth, "{\n")
-      keys = item1.keys()
+      keys = sorted(item1.keys())
       for keys_count, (key) in enumerate(keys, 1):
         if key == 'items':
           self._AddIndentedNontranslateableChunk(depth + 1, "\"items\": [\n")