Add support for flow traces in fml/trace_event. (flutter#3903)

Author: chinmaygarde

fml/trace_event.cc

@@ -136,5 +136,42 @@ void TraceEventInstant0(TraceArg category_group, TraceArg name) {
                      );
 }
 
+void TraceEventFlowBegin0(TraceArg category_group,
+                          TraceArg name,
+                          TraceIDArg id) {
+  Dart_TimelineEvent(name,                            // label
+                     Dart_TimelineGetMicros(),        // timestamp0
+                     id,                              // timestamp1_or_async_id
+                     Dart_Timeline_Event_Flow_Begin,  // event type
+                     0,                               // argument_count
+                     nullptr,                         // argument_names
+                     nullptr                          // argument_values
+                     );
+}
+
+void TraceEventFlowStep0(TraceArg category_group,
+                         TraceArg name,
+                         TraceIDArg id) {
+  Dart_TimelineEvent(name,                           // label
+                     Dart_TimelineGetMicros(),       // timestamp0
+                     id,                             // timestamp1_or_async_id
+                     Dart_Timeline_Event_Flow_Step,  // event type
+                     0,                              // argument_count
+                     nullptr,                        // argument_names
+                     nullptr                         // argument_values
+                     );
+}
+
+void TraceEventFlowEnd0(TraceArg category_group, TraceArg name, TraceIDArg id) {
+  Dart_TimelineEvent(name,                          // label
+                     Dart_TimelineGetMicros(),      // timestamp0
+                     id,                            // timestamp1_or_async_id
+                     Dart_Timeline_Event_Flow_End,  // event type
+                     0,                             // argument_count
+                     nullptr,                       // argument_names
+                     nullptr                        // argument_values
+                     );
+}
+
 }  // namespace tracing
 }  // namespace fml

fml/trace_event.h

@@ -45,6 +45,15 @@
 #define TRACE_EVENT_INSTANT0(category_group, name) \
   ::fml::tracing::TraceEventInstant0(category_group, name);
 
+#define TRACE_FLOW_BEGIN(category, name, id, args...) \
+  ::fml::tracing::TraceEventFlowBegin0(category, name, id);
+
+#define TRACE_FLOW_STEP(category, name, id, args...) \
+  ::fml::tracing::TraceEventFlowStep0(category, name, id);
+
+#define TRACE_FLOW_END(category, name, id, args...) \
+  ::fml::tracing::TraceEventFlowEnd0(category, name, id);
+
 #endif  // TRACE_EVENT_HIDE_MACROS
 
 namespace fml {
@@ -89,6 +98,14 @@ void TraceEventAsyncEnd1(TraceArg category_group,
 
 void TraceEventInstant0(TraceArg category_group, TraceArg name);
 
+void TraceEventFlowBegin0(TraceArg category_group,
+                          TraceArg name,
+                          TraceIDArg id);
+
+void TraceEventFlowStep0(TraceArg category_group, TraceArg name, TraceIDArg id);
+
+void TraceEventFlowEnd0(TraceArg category_group, TraceArg name, TraceIDArg id);
+
 class ScopedInstantEnd {
  public:
   ScopedInstantEnd(std::string str) : label_(std::move(str)) {}