[Fuchsia] Routes timeline events to Fuchsia's tracing app

runtime/vm/timeline.h

Index: runtime/vm/timeline.h
diff --git a/runtime/vm/timeline.h b/runtime/vm/timeline.h
index c7c6016693bd9489884608cbbb4e415f3cd322a1..ced35809e6f32e4a0a020620894aacb7859dafcd 100644
--- a/runtime/vm/timeline.h
+++ b/runtime/vm/timeline.h
@@ -318,6 +318,10 @@ class TimelineEvent {
   // Returns the number of bytes written into |buffer|.
   intptr_t PrintSystrace(char* buffer, intptr_t buffer_size);
 
+#if defined(HOST_OS_FUCHSIA)
+  void EmitFuchsiaEvent();
+#endif
+
  private:
   void FreeArguments();
 
@@ -433,6 +437,10 @@ class TimelineEventScope : public StackResource {
 
   const char* label() const { return label_; }
 
+  TimelineEventArgument* arguments() const { return arguments_; }
+
+  intptr_t arguments_length() const { return arguments_length_; }
+
   TimelineStream* stream() const { return stream_; }
 
   virtual ~TimelineEventScope();