Added isolate + thread high watermark tracking to Observatory

runtime/vm/thread.h

Index: runtime/vm/thread.h
diff --git a/runtime/vm/thread.h b/runtime/vm/thread.h
index 576d57c19d1e637908acb34d5fd4a7c721f421cb..410f7a120d2412640da515e0e27445e377d681f7 100644
--- a/runtime/vm/thread.h
+++ b/runtime/vm/thread.h
@@ -264,6 +264,26 @@ class Thread : public BaseThread {
 
   bool ZoneIsOwnedByThread(Zone* zone) const;
 
+  void IncrementThreadMemoryUsage(intptr_t value) {
+    current_thread_memory_ += value;
+    if (current_thread_memory_ > thread_memory_high_watermark_) {
+      thread_memory_high_watermark_ = current_thread_memory_;
+    }
+  }
+
+  void DecrementThreadMemoryUsage(intptr_t value) {
+    current_thread_memory_ -= value;
+  }
+
+  intptr_t GetThreadHighWatermark() const {
+    return thread_memory_high_watermark_;
+  }
+
+  void ClearThreadMemoryUsageStats() {
+    thread_memory_high_watermark_ = 0;
+    current_thread_memory_ = 0;
+  }
+
   // The reusable api local scope for this thread.
   ApiLocalScope* api_reusable_scope() const { return api_reusable_scope_; }
   void set_api_reusable_scope(ApiLocalScope* value) {
@@ -679,6 +699,8 @@ class Thread : public BaseThread {
   OSThread* os_thread_;
   Monitor* thread_lock_;
   Zone* zone_;
+  intptr_t current_thread_memory_;
+  intptr_t thread_memory_high_watermark_;
   ApiLocalScope* api_reusable_scope_;
   ApiLocalScope* api_top_scope_;
   StackResource* top_resource_;