Add the streamListen and streamCancel rpcs to the vm service.

runtime/observatory/lib/src/elements/heap_profile.dart

Index: runtime/observatory/lib/src/elements/heap_profile.dart
diff --git a/runtime/observatory/lib/src/elements/heap_profile.dart b/runtime/observatory/lib/src/elements/heap_profile.dart
index 5e097e5e7a0d5606f021059ca333691a3d9b1013..bd9fafae8fb667dda5919553715280f11d2f7386 100644
--- a/runtime/observatory/lib/src/elements/heap_profile.dart
+++ b/runtime/observatory/lib/src/elements/heap_profile.dart
@@ -94,7 +94,7 @@ class HeapProfileElement extends ObservatoryElement {
     _oldPieChart = new Chart('PieChart',
         shadowRoot.querySelector('#oldPieChart'));
     _classTableBody = shadowRoot.querySelector('#classTableBody');
-    _subscription = app.vm.events.stream.where(
+    _subscription = app.vm.gcEvents.where(
         (event) => event.isolate == isolate).listen(_onEvent);
   }