Added isolate + thread high watermark tracking to Observatory

runtime/vm/zone.cc

Index: runtime/vm/zone.cc
diff --git a/runtime/vm/zone.cc b/runtime/vm/zone.cc
index 36e962260dd30ed433c67ff89812392ece46ec04..6d48e9a233c89029610c34710bb32df9b8ee684c 100644
--- a/runtime/vm/zone.cc
+++ b/runtime/vm/zone.cc
@@ -43,7 +43,13 @@ class Zone::Segment {
 
 void Zone::Segment::DeleteSegmentList(Segment* head) {
   Segment* current = head;
+  Thread* current_thread = Thread::Current();
   while (current != NULL) {
+    if (current_thread != NULL) {
+      // TODO(bkonyi) Handle special case of segment deletion within native
+      // isolate.
+      Thread::Current()->DecrementThreadMemoryUsage(current->size());
+    }
     Segment* next = current->next();
 #ifdef DEBUG
     // Zap the entire current segment (including the header).
@@ -68,6 +74,11 @@ Zone::Segment* Zone::Segment::New(intptr_t size, Zone::Segment* next) {
 #endif
   result->next_ = next;
   result->size_ = size;
+  if (Thread::Current() != NULL) {
+    // TODO(bkonyi) Handle special case of segment creation within native
+    // isolate.
+    Thread::Current()->IncrementThreadMemoryUsage(size);
+  }
   return result;
 }