tracing: ensure __metadata events are always added to the trace

base/trace_event/trace_log.cc

Index: base/trace_event/trace_log.cc
diff --git a/base/trace_event/trace_log.cc b/base/trace_event/trace_log.cc
index cc40ba98eb31f5c0b5e370bacbf8ca5b232a15dd..fc427fc5a5257db237d51fd3421850497a012ea3 100644
--- a/base/trace_event/trace_log.cc
+++ b/base/trace_event/trace_log.cc
@@ -479,6 +479,12 @@ void TraceLog::UpdateCategoryGroupEnabledFlag(size_t category_index) {
   }
 #endif
 
+  // TODO(primiano): this is a temporary workaround for catapult:#2341,
+  // to guarantee that metadata events are always added even if the category
+  // filter is "-*". See crbug.com/618054 for more details and long-term fix.
+  if (mode_ == RECORDING_MODE && !strcmp(category_group, "__metadata"))
+    enabled_flag |= ENABLED_FOR_RECORDING;
+
   g_category_group_enabled[category_index] = enabled_flag;
 }