Move EmbedderHeapTracer::TracePrologue call to the beginning of full gc

src/heap/mark-compact.cc

Index: src/heap/mark-compact.cc
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index a1736e9728a13ef05dff6e0c7da218d26cf271ca..aaa65f5e96a5fb28d312506fc5bafa9041c3c227 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -857,9 +857,18 @@ void MarkCompactCollector::Prepare() {
     AbortWeakCells();
     AbortTransitionArrays();
     AbortCompaction();
+    if (heap_->UsingEmbedderHeapTracer()) {
+      heap_->mark_compact_collector()->embedder_heap_tracer()->AbortTracing();
+    }
     was_marked_incrementally_ = false;
   }
 
+  if (!was_marked_incrementally_) {
+    if (heap_->UsingEmbedderHeapTracer()) {
+      heap_->mark_compact_collector()->embedder_heap_tracer()->TracePrologue();
+    }
+  }
+
   // Don't start compaction if we are in the middle of incremental
   // marking cycle. We did not collect any slots.
   if (!FLAG_never_compact && !was_marked_incrementally_) {
@@ -2320,10 +2329,6 @@ void MarkCompactCollector::MarkLiveObjects() {
     {
       TRACE_GC(heap()->tracer(),
                GCTracer::Scope::MC_MARK_WEAK_CLOSURE_EPHEMERAL);
-      if (UsingEmbedderHeapTracer()) {
-        embedder_heap_tracer()->TracePrologue();
-        ProcessMarkingDeque();
-      }
       ProcessEphemeralMarking(&root_visitor, false);
     }