[heap] Added fine grained timers to MC_MARK_WEAK_CLOSURE.

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 affe13d873e0f403895ce4f39647e64a622b5035..cadb68834b4181892353bebc03a2d79119d4f71f 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -2142,7 +2142,12 @@ void MarkCompactCollector::MarkLiveObjects() {
     // The objects reachable from the roots are marked, yet unreachable
     // objects are unmarked.  Mark objects reachable due to host
     // application specific logic or through Harmony weak maps.
-    ProcessEphemeralMarking(&root_visitor, false);
+    {
+      GCTracer::Scope gc_scope(heap()->tracer(),
+                               GCTracer::Scope::MC_MARK_WEAK_CLOSURE_EPHEMERAL);
+      ProcessEphemeralMarking(&root_visitor, false);
+      ProcessMarkingDeque();
+    }
 
     // The objects reachable from the roots, weak maps or object groups
     // are marked. Objects pointed to only by weak global handles cannot be
@@ -2151,18 +2156,33 @@ void MarkCompactCollector::MarkLiveObjects() {
     //
     // First we identify nonlive weak handles and mark them as pending
     // destruction.
-    heap()->isolate()->global_handles()->IdentifyWeakHandles(
-        &IsUnmarkedHeapObject);
+    {
+      GCTracer::Scope gc_scope(
+          heap()->tracer(), GCTracer::Scope::MC_MARK_WEAK_CLOSURE_WEAK_HANDLES);
+      heap()->isolate()->global_handles()->IdentifyWeakHandles(
+          &IsUnmarkedHeapObject);
+      ProcessMarkingDeque();
+    }
     // Then we mark the objects.
-    heap()->isolate()->global_handles()->IterateWeakRoots(&root_visitor);
-    ProcessMarkingDeque();
+
+    {
+      GCTracer::Scope gc_scope(
+          heap()->tracer(), GCTracer::Scope::MC_MARK_WEAK_CLOSURE_WEAK_ROOTS);
+      heap()->isolate()->global_handles()->IterateWeakRoots(&root_visitor);
+      ProcessMarkingDeque();
+    }
 
     // Repeat Harmony weak maps marking to mark unmarked objects reachable from
     // the weak roots we just marked as pending destruction.
     //
     // We only process harmony collections, as all object groups have been fully
     // processed and no weakly reachable node can discover new objects groups.
-    ProcessEphemeralMarking(&root_visitor, true);
+    {
+      GCTracer::Scope gc_scope(heap()->tracer(),
+                               GCTracer::Scope::MC_MARK_WEAK_CLOSURE_HARMONY);
+      ProcessEphemeralMarking(&root_visitor, true);
+      ProcessMarkingDeque();
+    }
   }
 
   if (FLAG_print_cumulative_gc_stat) {