[Extensions] Add feature documentation for contexts

extensions/common/features/feature.h

 // Copyright 2013 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.
 
 #ifndef EXTENSIONS_COMMON_FEATURES_FEATURE_H_
 #define EXTENSIONS_COMMON_FEATURES_FEATURE_H_
 
 #include <set>
 #include <string>
 
@@ skipping 11 matching lines @@
 // top-level manifest key, a permission, or a programmatic API. A feature can
 // express requirements for where it can be accessed, and supports testing
 // support for those requirements. If platforms are not specified, then feature
 // is available on all platforms.
 class Feature {
  public:
   // The JavaScript contexts the feature is supported in.
   enum Context {
     UNSPECIFIED_CONTEXT,
 
-    // A context in a privileged extension process.
+    // See chrome/common/extensions/api/_features.md for a description of these
+    // contexts.
     BLESSED_EXTENSION_CONTEXT,
-
-    // A context in an unprivileged extension process.
     UNBLESSED_EXTENSION_CONTEXT,
-
-    // A context from a content script.
     CONTENT_SCRIPT_CONTEXT,
-
-    // A normal web page. This should have an associated URL matching pattern.
     WEB_PAGE_CONTEXT,
-
-    // A web page context which has been blessed by the user. Typically this
-    // will be via the installation of a hosted app, so this may host an
-    // extension. This is not affected by the URL matching pattern.
     BLESSED_WEB_PAGE_CONTEXT,
-
-    // A page within webui.
     WEBUI_CONTEXT,
-
-    // A context belonging to a service worker.
     SERVICE_WORKER_CONTEXT,
   };
 
   // The platforms the feature is supported in.
   enum Platform {
     UNSPECIFIED_PLATFORM,
     CHROMEOS_PLATFORM,
     LINUX_PLATFORM,
     MACOSX_PLATFORM,
     WIN_PLATFORM
@@ skipping 100 matching lines @@
  protected:
   std::string name_;
   bool no_parent_;
   // TODO(devlin): Remove this once we set the feature channel for tests.
   bool check_channel_;
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_FEATURES_FEATURE_H_