Support requesting subsets of host permissions using the permissions API.

chrome/common/extensions/permissions/permission_set.h

 // Copyright (c) 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.
 
 #ifndef CHROME_COMMON_EXTENSIONS_PERMISSIONS_PERMISSION_SET_H_
 #define CHROME_COMMON_EXTENSIONS_PERMISSIONS_PERMISSION_SET_H_
 
 #include <map>
 #include <set>
 #include <string>
@@ skipping 49 matching lines @@
   static PermissionSet* CreateUnion(
       const PermissionSet* set1, const PermissionSet* set2);
 
   // Creates a new permission set that only contains permissions that must be
   // in the manifest.  Passes ownership of the new set to the caller.
   static PermissionSet* ExcludeNotInManifestPermissions(
       const PermissionSet* set);
 
   bool operator==(const PermissionSet& rhs) const;
 
-  // Returns true if |set| is a subset of this.
+  // Returns true if every API or host permission available to |set| is also
+  // available to this. In other words, if the API permissions of |set| are a
+  // subset of this, and the host permissions in this encompass those in |set|.
   bool Contains(const PermissionSet& set) const;
 
   // Gets the API permissions in this set as a set of strings.
   std::set<std::string> GetAPIsAsStrings() const;
 
   // Returns whether this namespace has any functions which the extension has
   // permission to use.  For example, even though the extension may not have
   // the "tabs" permission, "tabs.create" requires no permissions so
   // HasAnyAccessToAPI("tabs") will return true.
   bool HasAnyAccessToAPI(const std::string& api_name) const;
@@ skipping 120 matching lines @@
   // TODO(jstritar): Rename to "user_script_hosts_"?
   URLPatternSet scriptable_hosts_;
 
   // The list of hosts this effectively grants access to.
   URLPatternSet effective_hosts_;
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_COMMON_EXTENSIONS_PERMISSIONS_PERMISSION_SET_H_