Bug 1646266 - NoPayload default type, with specialized empty helper - r=gregtatum

`NoPayload` will be mostly used internally when adding markers without payload data.
It has an empty specialization of the MarkerTypeHelper (mainly to catch misuses), and the add-marker code will need to have different compile-time paths to handle it.

Differential Revision: https://phabricator.services.mozilla.com/D87252

mozglue/baseprofiler/public/BaseProfilerMarkersDetail.h

@@ -93,6 +93,11 @@ struct MarkerTypeSerialization {
       std::tuple_element_t<i, StreamFunctionUserParametersTuple>;
 };
 
+template <>
+struct MarkerTypeSerialization<::mozilla::baseprofiler::markers::NoPayload> {
+  // Nothing! NoPayload has special handling avoiding payload work.
+};
+
 }  // namespace mozilla::base_profiler_markers_detail
 
 namespace mozilla {

mozglue/baseprofiler/public/BaseProfilerMarkersPrerequisites.h

@@ -633,6 +633,14 @@ MarkerOptions MarkerCategory::WithOptions(Options&&... aOptions) const {
 
 }  // namespace mozilla
 
+namespace mozilla::baseprofiler::markers {
+
+// Default marker payload types, with no extra information, not even a marker
+// type and payload. This is intended for label-only markers.
+struct NoPayload final {};
+
+}  // namespace mozilla::baseprofiler::markers
+
 #endif  // MOZ_GECKO_PROFILER
 
 #endif  // BaseProfilerMarkersPrerequisites_h

tools/profiler/public/ProfilerMarkersPrerequisites.h

@@ -17,6 +17,14 @@
 
 #ifdef MOZ_GECKO_PROFILER
 
+namespace profilermarkers {
+
+// Default marker payload types, with no extra information, not even a marker
+// type and payload. This is intended for label-only markers.
+using NoPayload = ::mozilla::baseprofiler::markers::NoPayload;
+
+}  // namespace profilermarkers
+
 #endif  // MOZ_GECKO_PROFILER
 
 #endif  // ProfilerMarkersPrerequisites_h