[heap] EphemeronHashTable in Incremental Marking

Mark values if their corresponding key was already marked. Also
take into account the size for backing store.

Bug: chromium:844008
Change-Id: I58570f935c69fb39b686fd22dc93caba309f83b2
Reviewed-on: https://chromium-review.googlesource.com/1097400Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@google.com>
Cr-Commit-Position: refs/heads/master@{#53690}

src/heap/incremental-marking.cc

@@ -16,6 +16,7 @@
 #include "src/heap/objects-visiting-inl.h"
 #include "src/heap/objects-visiting.h"
 #include "src/heap/sweeper.h"
+#include "src/objects/hash-table-inl.h"
 #include "src/tracing/trace-event.h"
 #include "src/v8.h"
 #include "src/visitors.h"

src/heap/mark-compact-inl.h

@@ -92,8 +92,16 @@ int MarkingVisitor<fixed_array_mode, retaining_path_mode, MarkingState>::
     VisitEphemeronHashTable(Map* map, EphemeronHashTable* table) {
   collector_->AddEphemeronHashTable(table);
 
-  // TODO(dinfuehr): Account size of the backing store.
-  return 0;
+  for (int i = 0; i < table->Capacity(); i++) {
+    HeapObject* key = HeapObject::cast(table->KeyAt(i));
+    if (marking_state()->IsBlackOrGrey(key)) {
+      Object** value_slot =
+          table->RawFieldOfElementAt(EphemeronHashTable::EntryToValueIndex(i));
+      VisitPointer(table, value_slot);
+    }
+  }
+
+  return table->SizeFromMap(map);
 }
 
 template <FixedArrayVisitationMode fixed_array_mode,