Bug 1688308 - Add a marker for "Perform microtasks". r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D102804

xpcom/base/CycleCollectedJSContext.cpp

@@ -19,6 +19,7 @@
 #include "mozilla/CycleCollectedJSRuntime.h"
 #include "mozilla/DebuggerOnGCRunnable.h"
 #include "mozilla/MemoryReporting.h"
+#include "mozilla/ProfilerMarkers.h"
 #include "mozilla/Sprintf.h"
 #include "mozilla/Telemetry.h"
 #include "mozilla/TimelineConsumers.h"
@@ -610,6 +611,8 @@ bool CycleCollectedJSContext::PerformMicroTaskCheckPoint(bool aForce) {
   MOZ_ASSERT(aForce ? currentDepth == 0 : currentDepth > 0);
   mMicroTaskRecursionDepth = currentDepth;
 
+  AUTO_PROFILER_TRACING_MARKER("JS", "Perform microtasks", JS);
+
   bool didProcess = false;
   AutoSlowOperation aso;