Added isolate + thread high watermark tracking to Observatory

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

Index: runtime/observatory/lib/src/models/objects/isolate.dart
diff --git a/runtime/observatory/lib/src/models/objects/isolate.dart b/runtime/observatory/lib/src/models/objects/isolate.dart
index 8cc5c79595548bc8abda9071b39484360cf08eb0..3c69fec1d12914e202888c05cd4a0d16c618506a 100644
--- a/runtime/observatory/lib/src/models/objects/isolate.dart
+++ b/runtime/observatory/lib/src/models/objects/isolate.dart
@@ -54,6 +54,11 @@ abstract class Isolate extends IsolateRef {
   /// The list of threads associated with this isolate.
   Iterable<Thread> get threads;
 
+  /// The maximum amount of memory in bytes allocated by the isolate in all
+  /// threads at a given time. Calculated using the high watermarks of each
+  /// thread alive when a thread is unscheduled.
+  int get memoryHighWatermark;
+
   /// The current pause on exception mode for this isolate.
   //ExceptionPauseMode get exceptionPauseMode;