Bug 1843534 - Avoid taking unnecessary timestamps when thread is not being profiled for markers. r=julienw

As taking timestamps can be expensive on certain devices we should try
to avoid taking them where possible. This patch fixes a few occasions
where we take a timestamp solely for a profiler marker even when the
current thread is not being profiled.

Differential Revision: https://phabricator.services.mozilla.com/D185008

layout/base/AutoProfilerStyleMarker.h

@@ -19,7 +19,6 @@ class MOZ_RAII AutoProfilerStyleMarker {
   explicit AutoProfilerStyleMarker(UniquePtr<ProfileChunkedBuffer> aCause,
                                    const Maybe<uint64_t>& aInnerWindowID)
       : mActive(profiler_thread_is_being_profiled_for_markers()),
-        mStartTime(TimeStamp::Now()),
         mCause(std::move(aCause)),
         mInnerWindowID(aInnerWindowID) {
     if (!mActive) {
@@ -29,6 +28,8 @@ class MOZ_RAII AutoProfilerStyleMarker {
                "Nested AutoProfilerStyleMarker");
     ServoTraversalStatistics::sSingleton = ServoTraversalStatistics();
     ServoTraversalStatistics::sActive = true;
+
+    mStartTime = TimeStamp::Now();
   }
 
   ~AutoProfilerStyleMarker() {

tools/profiler/public/ProfilerMarkers.h

@@ -260,6 +260,9 @@ class MOZ_RAII AutoProfilerTracing {
         mMarkerName(aMarkerName),
         mCategoryPair(aCategoryPair),
         mInnerWindowID(aInnerWindowID) {
+    if (!profiler_thread_is_being_profiled_for_markers()) {
+      return;
+    }
     profiler_add_marker(
         mozilla::ProfilerString8View::WrapNullTerminatedString(mMarkerName),
         mCategoryPair,
@@ -279,6 +282,9 @@ class MOZ_RAII AutoProfilerTracing {
         mMarkerName(aMarkerName),
         mCategoryPair(aCategoryPair),
         mInnerWindowID(aInnerWindowID) {
+    if (!profiler_thread_is_being_profiled_for_markers()) {
+      return;
+    }
     profiler_add_marker(
         mozilla::ProfilerString8View::WrapNullTerminatedString(mMarkerName),
         mCategoryPair,
@@ -291,6 +297,9 @@ class MOZ_RAII AutoProfilerTracing {
   }
 
   ~AutoProfilerTracing() {
+    if (!profiler_thread_is_being_profiled_for_markers()) {
+      return;
+    }
     profiler_add_marker(
         mozilla::ProfilerString8View::WrapNullTerminatedString(mMarkerName),
         mCategoryPair,