Re-apply 2d07fd7 more conservatively.

I think this matches up more precisely with the original intention, though I
may be completely wrong.  Notably though, this leaves out the rehashing which
uses kJSWeakCollectionLoadFactorExp.

deps/v8/src/objects.cc

@@ -14667,6 +14667,7 @@ Handle<CompilationCacheTable> CompilationCacheTable::PutRegExp(
 void CompilationCacheTable::Age() {
   DisallowHeapAllocation no_allocation;
   Object* the_hole_value = GetHeap()->the_hole_value();
+  uint32_t capacity = Capacity();
   for (int entry = 0, size = Capacity(); entry < size; entry++) {
     int entry_index = EntryToIndex(entry);
     int value_index = entry_index + 1;
@@ -14690,6 +14691,16 @@ void CompilationCacheTable::Age() {
       }
     }
   }
+  // Wipe deleted entries.
+  Heap* heap = GetHeap();
+  Object* the_hole = heap->the_hole_value();
+  Object* undefined = heap->undefined_value();
+  for (uint32_t current = 0; current < capacity; current++) {
+    if (get(EntryToIndex(current)) == the_hole) {
+      set(EntryToIndex(current), undefined);
+    }
+  }
+  SetNumberOfDeletedElements(0);
 }
 
 
@@ -15212,6 +15223,12 @@ Handle<ObjectHashTable> ObjectHashTable::Put(Handle<ObjectHashTable> table,
     }
   }
 
+  // Rehash if more than 25% of the entries are deleted entries.
+  // TODO(jochen): Consider to shrink the fixed array in place.
+  if ((table->NumberOfDeletedElements() << 1) > table->NumberOfElements()) {
+    table->Rehash(isolate->factory()->undefined_value());
+  }
+
   // Check whether the hash table should be extended.
   table = EnsureCapacity(table, 1, key);
   table->AddEntry(table->FindInsertionEntry(hash), *key, *value);

deps/v8/test/cctest/test-weakmaps.cc

@@ -123,7 +123,7 @@ TEST(Weakness) {
   heap->CollectAllGarbage(false);
   CHECK_EQ(1, NumberOfWeakCalls);
   CHECK_EQ(0, ObjectHashTable::cast(weakmap->table())->NumberOfElements());
-  CHECK_EQ(2,
+  CHECK_EQ(0,
            ObjectHashTable::cast(weakmap->table())->NumberOfDeletedElements());
 }
 

deps/v8/test/cctest/test-weaksets.cc

@@ -122,8 +122,8 @@ TEST(WeakSet_Weakness) {
   heap->CollectAllGarbage(false);
   CHECK_EQ(1, NumberOfWeakCalls);
   CHECK_EQ(0, ObjectHashTable::cast(weakset->table())->NumberOfElements());
-  CHECK_EQ(
-      1, ObjectHashTable::cast(weakset->table())->NumberOfDeletedElements());
+  CHECK_EQ(0,
+           ObjectHashTable::cast(weakset->table())->NumberOfDeletedElements());
 }