Improve display of simd vector types and stack traces in Observatory.

runtime/vm/service/service.md

 # Dart VM Service Protocol 2.0
 
 > Please post feedback to the [observatory-discuss group][discuss-list]
 
 This document describes of _version 2.0_ 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,
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   @Class class;
 
   // The value of this instance as a string.
   //
   // Provided for the instance kinds:
   //   Null (null)
   //   Bool (true or false)
   //   Double (suitable for passing to Double.parse())
   //   Int (suitable for passing to int.parse())
   //   String (value may be truncated)
+  //   Float32x4
+  //   Float64x2
+  //   Int32x4
+  //   StackTrace
   string valueAsString [optional];
 
   // The valueAsString for String references may be truncated. If so,
   // this property is added with the value 'true'.
   bool valueAsStringIsTruncated [optional];
 
   // The length of a List instance.
   //
   // Provided for instance kinds:
   //   List
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   String,
 
   // An instance of the built-in VM List implementation. User-defined
   // Lists will be PlainInstance.
   List,
 
   // An instance of the built-in VM Map implementation. User-defined
   // Maps will be PlainInstance.
   Map,
 
+  // Vector instance kinds.
+  Float32x4,
+  Float64x2,
+  Int32x4
+
   // An instance of the built-in VM TypedData implementations.  User-defined
   // TypedDatas will be PlainInstance.
   Uint8ClampedList,
   Uint8List,
   Uint16List,
   Uint32List,
   Uint64List,
   Int8List,
   Int16List,
   Int32List,
   Int64List,
   Float32List,
   Float64List,
   Int32x4List,
   Float32x4List,
   Float64x2List,
 
+  // An instance of the Dart class StackTrace.
+  StackTrace,
+
   // An instance of the built-in VM Closure implementation. User-defined
   // Closures will be PlainInstance.
   Closure,
 
   // An instance of the Dart class MirrorReference.
   MirrorReference,
 
   // An instance of the Dart class RegExp.
   RegExp,
 
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 ```
 
 ## Revision History
 
 version | comments
 ------- | --------
 1.0 draft 1 | initial revision
 
 
 [discuss-list]: https://groups.google.com/a/dartlang.org/forum/#!forum/observatory-discuss