[Extension DocServer] Remove availability warning for enums

The availability warning for enums isn't really that helpful, since if an enum
is added somewhere, the availability warning will be on wherever it is used.

BUG=474980

Review URL: https://codereview.chromium.org/1070873002

Cr-Commit-Position: refs/heads/master@{#324287}

chrome/common/extensions/docs/server2/app.yaml

 application: chrome-apps-doc
-version: 3-48-2
+version: 3-49-0
 runtime: python27
 api_version: 1
 threadsafe: false

chrome/common/extensions/docs/server2/cron.yaml

@@ -2,4 +2,4 @@ cron:
 - description: Repopulates all cached data.
   url: /_cron
   schedule: every 180 minutes
-  target: 3-48-2
+  target: 3-49-0

chrome/common/extensions/docs/server2/jsc_view.py

@@ -233,7 +233,8 @@ class _JSCViewBuilder(object):
         'functions': self._GenerateFunctions(type_.functions),
         'events': self._GenerateEvents(type_.events),
         'id': _CreateId(type_, 'type'),
-        'availability': self._GetAvailabilityTemplate()
+        'availability': self._GetAvailabilityTemplate(
+            is_enum=type_.property_type == model.PropertyType.ENUM)
       }
       self._RenderTypeInformation(type_, type_dict)
       return type_dict
@@ -444,10 +445,16 @@ class _JSCViewBuilder(object):
       'version': version
     }
 
-  def _GetAvailabilityTemplate(self):
+  def _GetAvailabilityTemplate(self, is_enum=False):
     '''Gets availability for the current node and returns an appropriate
     template object.
     '''
+    # We don't show an availability warning for enums.
+    # TODO(devlin): We should also render enums differently, indicating that
+    # symbolic constants are available from version 44 onwards.
+    if is_enum:
+      return None
+
     # Displaying deprecated status takes precedence over when the API
     # became stable.
     availability_info = self._current_node.GetDeprecated()