VM: Make indirect subclasses of StackResource have virtual destructor

runtime/vm/timeline.h

Index: runtime/vm/timeline.h
diff --git a/runtime/vm/timeline.h b/runtime/vm/timeline.h
index cc93040798dbfe3de32d885d8e015c120b518e10..4b4333e02aea8714d0d8ba89e9bc4fe19799d985 100644
--- a/runtime/vm/timeline.h
+++ b/runtime/vm/timeline.h
@@ -461,7 +461,7 @@ class TimelineDurationScope : public TimelineEventScope {
                         TimelineStream* stream,
                         const char* label);
 
-  ~TimelineDurationScope();
+  virtual ~TimelineDurationScope();
 
  private:
   int64_t timestamp_;
@@ -479,7 +479,7 @@ class TimelineBeginEndScope : public TimelineEventScope {
                         TimelineStream* stream,
                         const char* label);
 
-  ~TimelineBeginEndScope();
+  virtual ~TimelineBeginEndScope();
 
  private:
   void EmitBegin();