Introduce kiosk.autolaunched feature session type

chrome/common/extensions/api/_features.md

 # Extension Features Files
 
 [TOC]
 
 ## Summary
 
 The Extension features files specify the different requirements for extension
 feature availability.
 
 An **extension feature** can be any component of extension capabilities. Most
@@ skipping 291 matching lines @@
 ### session\_types
 
 The `session_types` property specifies in which types of sessions a feature
 should be available. The session type describes the type of user that is
 logged in the current session. Session types to which feature can be restricted
 are only supported on Chrome OS - features restricted to set of session types
 will be disabled on other platforms. Also, note that all currently supported
 session types imply that a user is logged into the session (i.e. features that
 use `session_types` property will be disabled when a user is not logged in).
 
-The accepted values are lists of strings from `regular` and `kiosk`.
+The accepted values are lists of strings from `regular`, `kiosk` and
+`kiosk.autolaunched`.
+
+`regular` session is a session launched for a regular, authenticated user.
+
+`kiosk` session is a session launched for a kiosk app - an app that runs on its
+own, in full control of the current session. 
+
+`kiosk.autolaunched` represents auto-launched kiosk session - a kiosk session
+that is launched automatically from Chrome OS login screen, without any user
+interaction. Note that allowing `kiosk` session implies allowing
+`kiosk.autolanched` session.

[achuithb, 2017/01/04 23:25:30]

autolaunched

[tbarzic, 2017/01/04 23:39:48]

Done.

 
 ### source
 
 The `source` property specifies that the feature is an alias for the feature
 specified by the property value, and is only allowed for API features.
-For more information about alias features, see [alias](#alias) property documentation.
+For more information about alias features, see [alias](#alias) property
+documentation.
 
 For complex features, `source` property will be set to the `source` value of the
 first component simple feature that has it set.
 
 ### whitelist
 
 The `whitelist` property specifies a list of ID hashes for extensions that
 are the only extensions allowed to access a feature.
 
 Accepted values are lists of id hashes.
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 at runtime, this has the added benefit of allowing us to validate at compile
 time rather than needing a unittest (or allowing incorrect features).
 
 In theory, invalid features should result in a compilation failure; in practice,
 the compiler is probably missing some cases.
 
 ## Still to come
 
 TODO(devlin): Add documentation for extension types. Probably also more on
 requirements for individual features.