[Extensions Bindings] Check availability of custom API properties

chrome/common/extensions/api/_api_features.json

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This features file defines extension APIs implemented under src/chrome.
 // See chrome/common/extensions/api/_features.md to understand this file, as
 // well as feature.h, simple_feature.h, and feature_provider.h.
 //
 // Note that specifying "web_page", "blessed_web_page", or "all" as a context
 // type will require manually updating chrome/renderer/resources/dispatcher.cc.
@@ skipping 651 matching lines @@
     "contexts": ["blessed_extension"]
   }],
   "preferencesPrivate": {
     "dependencies": ["permission:preferencesPrivate"],
     "contexts": ["blessed_extension"]
   },
   "privacy": {
     "dependencies": ["permission:privacy"],
     "contexts": ["blessed_extension"]
   },
+  "privacy.websites.protectedContentEnabled": {

[jbroman, 2017/06/27 19:49:57]

Does this mean you intend to deprecate the explicit "platforms" field in the
individual API .json files? The legacy code seems to use isSchemaNodeSupported
to manage this.

+    "platforms": ["chromeos", "win"]
+  },
   "processes": {
     "dependencies": ["permission:processes"],
     "contexts": ["blessed_extension"]
   },
   "proxy": {
     "dependencies": ["permission:proxy"],
     "contexts": ["blessed_extension"]
   },
   "imageWriterPrivate": {
     "dependencies": ["permission:imageWriterPrivate"],
@@ skipping 163 matching lines @@
     "dependencies": ["api:tabs"],
     "contexts": ["blessed_extension"]
   }, {
     "channel": "stable",
     "contexts": ["webui"],
     "matches": [
       "chrome://bookmarks/*"
     ]
   }]
 }