Simple BlinkGC heap compaction.

third_party/WebKit/Source/wtf/HashTable.h

Index: third_party/WebKit/Source/wtf/HashTable.h
diff --git a/third_party/WebKit/Source/wtf/HashTable.h b/third_party/WebKit/Source/wtf/HashTable.h
index c3735e9de3dea61026237f229babb370be8a90c0..9bceee0450cc562d8355f4bc68479f51cb3074a9 100644
--- a/third_party/WebKit/Source/wtf/HashTable.h
+++ b/third_party/WebKit/Source/wtf/HashTable.h
@@ -2092,6 +2092,7 @@ void HashTable<Key,
   // place after we know if the backing is reachable from elsewhere. We also
   // register a weakProcessing callback which will perform weak processing if
   // needed.
+
   if (Traits::weakHandlingFlag == NoWeakHandlingInCollections) {
     Allocator::markNoTracing(visitor, m_table);
   } else {
@@ -2105,6 +2106,10 @@ void HashTable<Key,
                                       Extractor, HashFunctions, Traits,
                                       KeyTraits, Allocator>::process);
   }
+  // If the backing store will be moved by sweep compaction, register the
+  // table reference pointing to the backing store object, so that the
+  // reference is updated upon object relocation.
+  Allocator::registerBackingStoreReference(visitor, &m_table);
   if (!IsTraceableInCollectionTrait<Traits>::value)
     return;
   if (Traits::weakHandlingFlag == WeakHandlingInCollections) {