Implement PermissionDescriptor usage in Permissions API.

Source/modules/permissions/PermissionDescriptor.idl

Index: Source/modules/permissions/PermissionDescriptor.idl
diff --git a/Source/modules/permissions/PermissionDescriptor.idl b/Source/modules/permissions/PermissionDescriptor.idl
new file mode 100644
index 0000000000000000000000000000000000000000..c77009956fa40f28d516403613fb212e016b5f20
--- /dev/null
+++ b/Source/modules/permissions/PermissionDescriptor.idl
@@ -0,0 +1,14 @@
+// Copyright 2015 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.
+
+enum PermissionName {
+    "geolocation",
+    "notifications",
+    "push",
+    "midi"

[whywhat, 2015/03/31 14:51:45]

nit: alphabetical order?

[mlamouri (slow - plz ping), 2015/03/31 20:24:46]

Done.

+};
+
+dictionary PermissionDescriptor {

[whywhat, 2015/03/31 14:51:44]

nit: comment, esp. that it's extendable by particular APIs for custom
permissions

[mlamouri (slow - plz ping), 2015/03/31 20:24:46]

Done.

+    /* required */ PermissionName name;

[whywhat, 2015/03/31 14:51:45]

why 'required' is commented out?

[mlamouri (slow - plz ping), 2015/03/31 20:24:46]

It's a WebIDL feature not implemented by Blink :(
I opened https://code.google.com/p/chromium/issues/detail?id=472220

+};