Mark script kinds as private in the service protocol.

runtime/vm/service/service.md

 # Dart VM Service Protocol 0.0
 
 This document describes _version 0.0_ of the Dart VM Service Protocol.
 This protocol is used to communicate with a running Dart Virtual
 Machine.
 
 To use the Service Protocol, start the VM with the *--observe* flag.
 The VM will start a webserver which services protocol requests via WebSocket.
 It is possible to make HTTP (non-WebSocket) requests,
 but this does not allow access to VM _events_ and is not documented
@@ skipping 1513 matching lines @@
 ```
 
 A _SentinelType_ is used to distinguish different kinds of _Sentinel_ objects.
 
 ### Script
 
 ```
 class @Script extends @Object {
   // The uri from which this script was loaded.
   string uri;
-
-  // What kind of script is this?
-  string kind;
 }
 ```
 
 _@Script_ is a reference to a _Script_.
 
 ```
 class Script extends Object {
   // The uri from which this script was loaded.
   string uri;
 
-  // What kind of script is this?
-  ScriptKind kind;
-
   // The library which owns this script.
   @Library library;
 
   // The source code for this script.  For certain built-in scripts,
   // this may be reconstructed without source comments.
   string source;
 
   // A table encoding a mapping from token position to line and column.
   int[][] tokenPosTable;
 }
@@ skipping 11 matching lines @@
 > [[1, 100, 5, 101, 8],[2, 102, 7]]
 
 ...encodes the mapping:
 
 tokenPos | line | column
 -------- | ---- | ------
 100 | 1 | 5
 101 | 1 | 8
 102 | 2 | 7
 
-### ScriptKind
-
-```
-enum ScriptKind {
-  script,
-  library,
-  source,
-  patch
-}
-```
-
-A _ScriptKind_ is used to classify a _Script_.
-
-TODO: We need to explain what this is about or find a way to hide it.
-
 ### Stack
 
 ```
 class Stack {
   Frame[] frames;
   Message[] messages;
 }
 ```
 
 ### StepOption
@@ skipping 165 matching lines @@
   // A list of isolates running in the VM.
   @Isolate[] isolates
 }
 ```
 
 ## Revision History
 
 version | comments
 ------- | --------
 0.0 | draft