Allow embedders to add events to the timeline.

Fixes flutter/flutter#28283

shell/platform/embedder/embedder.cc

@@ -24,6 +24,7 @@
 #include "flutter/fml/make_copyable.h"
 #include "flutter/fml/message_loop.h"
 #include "flutter/fml/paths.h"
+#include "flutter/fml/trace_event.h"
 #include "flutter/shell/common/rasterizer.h"
 #include "flutter/shell/common/switches.h"
 #include "flutter/shell/platform/embedder/embedder.h"
@@ -801,3 +802,15 @@ FlutterEngineResult FlutterEngineDispatchSemanticsAction(
   }
   return kSuccess;
 }
+
+void FlutterEngineTraceEventDurationBegin(const char* name) {
+  fml::tracing::TraceEvent0("flutter", name);
+}
+
+void FlutterEngineTraceEventDurationEnd(const char* name) {
+  fml::tracing::TraceEventEnd(name);
+}
+
+void FlutterEngineTraceEventInstant(const char* name) {
+  fml::tracing::TraceEventInstant0("flutter", name);
+}

shell/platform/embedder/embedder.h

@@ -592,6 +592,28 @@ FlutterEngineResult FlutterEngineDispatchSemanticsAction(
     const uint8_t* data,
     size_t data_length);
 
+// A profiling utility. Logs a trace duration begin event to the timeline. If
+// the timeline is not available or disabled, this has no effect. Must be
+// balanced with an duration end event (via
+// |FlutterEngineTraceEventDurationEnd|) with the same name on the same thread.
+// Can be called on any thread.
+FLUTTER_EXPORT
+void FlutterEngineTraceEventDurationBegin(const char* name);
+
+// A profiling utility. Logs a trace duration end event to the timeline. If
+// the timeline is not available or disabled, this has no effect. This call must
+// be preceeded by a trace duration begin call (via
+// FlutterEngineTraceEventDurationBegin) with the same name on the same thread.
+// Can be called on any thread.
+FLUTTER_EXPORT
+void FlutterEngineTraceEventDurationEnd(const char* name);
+
+// A profiling utility. Logs a trace duration instant event to the timeline. If
+// the timeline is not available or disabled, this has no effect. Can be called
+// on any thread.
+FLUTTER_EXPORT
+void FlutterEngineTraceEventInstant(const char* name);
+
 #if defined(__cplusplus)
 }  // extern "C"
 #endif