Reland of "[heap] Tracer: Handle incremental marking scopes"

src/heap/incremental-marking.cc

Index: src/heap/incremental-marking.cc
diff --git a/src/heap/incremental-marking.cc b/src/heap/incremental-marking.cc
index 321d443caef7603b1cbad727a2e1ff7a34a457d2..f8f19d49967ef2d32956b88cb69cd7fbe6b15451 100644
--- a/src/heap/incremental-marking.cc
+++ b/src/heap/incremental-marking.cc
@@ -557,6 +557,8 @@ void IncrementalMarking::StartMarking() {
   state_ = MARKING;
 
   if (heap_->UsingEmbedderHeapTracer()) {
+    TRACE_GC(heap()->tracer(),
+             GCTracer::Scope::MC_INCREMENTAL_WRAPPER_PROLOGUE);
     heap_->mark_compact_collector()->embedder_heap_tracer()->TracePrologue();
   }
 
@@ -622,6 +624,9 @@ void IncrementalMarking::MarkRoots() {
 
 
 void IncrementalMarking::MarkObjectGroups() {
+  TRACE_GC(heap_->tracer(),
+           GCTracer::Scope::MC_INCREMENTAL_FINALIZE_OBJECT_GROUPING);
+
   DCHECK(!heap_->UsingEmbedderHeapTracer());
   DCHECK(!finalize_marking_completed_);
   DCHECK(IsMarking());
@@ -1203,6 +1208,8 @@ intptr_t IncrementalMarking::Step(intptr_t allocated_bytes,
       bytes_processed = ProcessMarkingDeque(bytes_to_process);
       if (FLAG_incremental_marking_wrappers &&
           heap_->UsingEmbedderHeapTracer()) {
+        TRACE_GC(heap()->tracer(),
+                 GCTracer::Scope::MC_INCREMENTAL_WRAPPER_TRACING);
         // This currently marks through all registered wrappers and does not
         // respect bytes_to_process.
         // TODO(hpayer): Integrate incremental marking of wrappers into