Fix many warnings/errors when building Observatory

runtime/observatory/lib/src/models/objects/thread.dart

Index: runtime/observatory/lib/src/models/objects/thread.dart
diff --git a/runtime/observatory/lib/src/models/objects/thread.dart b/runtime/observatory/lib/src/models/objects/thread.dart
index be461fdf4845fe97653cee7ceab584f38cdf5fde..8d16a8ce56c4fbecafe7f6f5a9170c59907bf99e 100644
--- a/runtime/observatory/lib/src/models/objects/thread.dart
+++ b/runtime/observatory/lib/src/models/objects/thread.dart
@@ -20,6 +20,8 @@ abstract class Thread {
   /// The task type associated with the thread.
   ThreadKind get kind;
 
+  String get kindString;
+
   /// The maximum amount of zone memory in bytes allocated by a thread at a
   /// given time throughout the entire life of the thread.
   int get zoneHighWatermark;