Added isolate + thread high watermark tracking to Observatory

runtime/observatory/lib/src/service/object.dart

Index: runtime/observatory/lib/src/service/object.dart
diff --git a/runtime/observatory/lib/src/service/object.dart b/runtime/observatory/lib/src/service/object.dart
index b9e0f6efd02e0dc4999bc1b9116b021199abc696..8025c0582374acbfde0a6ca9140ee47557793ef9 100644
--- a/runtime/observatory/lib/src/service/object.dart
+++ b/runtime/observatory/lib/src/service/object.dart
@@ -1507,6 +1507,9 @@ class Isolate extends ServiceObjectOwner implements M.Isolate {
   List<Thread> get threads => _threads;
   final List<Thread> _threads = new List<Thread>();
 
+  int get memoryHighWatermark => _memoryHighWatermark;
+  int _memoryHighWatermark;
+
   void _loadHeapSnapshot(ServiceEvent event) {
     if (_snapshotFetch == null || _snapshotFetch.isClosed) {
       // No outstanding snapshot request. Presumably another client asked for a
@@ -1632,9 +1635,11 @@ class Isolate extends ServiceObjectOwner implements M.Isolate {
     }
 
     threads.clear();
-    if(map['threads'] != null) {
-      threads.addAll(map['threads']);
+    if(map['_threads'] != null) {
+      threads.addAll(map['_threads']);
     }
+
+    _memoryHighWatermark = int.parse(map['_memoryHighWatermark']);
   }
 
   Future<TagProfile> updateTagProfile() {
@@ -3072,6 +3077,8 @@ class Thread extends ServiceObject implements M.Thread {
   M.ThreadKind _kind;
   String get kindString => _kindString;
   String _kindString;
+  int get memoryHighWatermark => _memoryHighWatermark;
+  int _memoryHighWatermark;
   List<Zone> get zones => _zones;
   final List<Zone> _zones = new List<Zone>();
 
@@ -3109,6 +3116,9 @@ class Thread extends ServiceObject implements M.Thread {
       default:
         assert(false);
     }
+
+    _memoryHighWatermark = int.parse(map['_memoryHighWatermark']);
+
     zones.clear();
     zoneList.forEach((zone) {
       int capacity = zone['capacity'];