Add API to set thread name

runtime/include/dart_tools_api.h

Index: runtime/include/dart_tools_api.h
diff --git a/runtime/include/dart_tools_api.h b/runtime/include/dart_tools_api.h
index 3f6a9c7f6f6dee976ec50c1ce93776f3e3b67f8c..da43d94f830187f432ec625bd885b3c83f6e9aff 100644
--- a/runtime/include/dart_tools_api.h
+++ b/runtime/include/dart_tools_api.h
@@ -991,7 +991,6 @@ typedef enum {
   Dart_Timeline_Event_Async_End,      // Phase = 'e'.
   Dart_Timeline_Event_Async_Instant,  // Phase = 'n'.
   Dart_Timeline_Event_Counter,        // Phase = 'C'.
-  Dart_Timeline_Event_Metadata,       // Phase = 'M'.
 } Dart_Timeline_Event_Type;
 
 /**
@@ -1014,6 +1013,14 @@ DART_EXPORT void Dart_TimelineEvent(const char* label,
                                     const char** argument_values);
 
 /**
+ * Associates a name with the current thread. This name will be used to name
+ * threads in the timeline. Can only be called after a call to Dart_Initialize.
+ *
+ * \param name The name of the thread.
+ */
+DART_EXPORT void Dart_SetThreadName(const char* name);
+
+/**
  * Called by the VM to let the embedder know when to start recording into the
  * timeline. Can be called from any thread.
  */