Make sure that NormalizeElements and ShouldConvertToFastElements are based on the same values

src/elements.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/elements.h"
 
 #include "src/arguments.h"
 #include "src/conversions.h"
 #include "src/factory.h"
 #include "src/messages.h"
@@ skipping 1209 matching lines @@
         for (i = entry + 1; i < length; i++) {
           if (!backing_store->is_the_hole(i)) break;
         }
         if (i == length) {
           DeleteAtEnd(obj, backing_store, entry);
           return;
         }
       }
       int num_used = 0;
       for (int i = 0; i < backing_store->length(); ++i) {
-        if (!backing_store->is_the_hole(i)) ++num_used;
-        // Bail out early if more than 1/4 is used.
-        if (4 * num_used > backing_store->length()) break;
+        if (!backing_store->is_the_hole(i)) {
+          ++num_used;
+          // Bail out if a number dictionary wouldn't be able to save at least
+          // 75% space.
+          if (4 * SeededNumberDictionary::ComputeCapacity(num_used) *
+                  SeededNumberDictionary::kEntrySize >
+              backing_store->length()) {
+            return;
+          }
+        }
       }
-      if (4 * num_used <= backing_store->length()) {
-        JSObject::NormalizeElements(obj);
-      }
+      JSObject::NormalizeElements(obj);
     }
   }
 
   static void ReconfigureImpl(Handle<JSObject> object,
                               Handle<FixedArrayBase> store, uint32_t entry,
                               Handle<Object> value,
                               PropertyAttributes attributes) {
     Handle<SeededNumberDictionary> dictionary =
         JSObject::NormalizeElements(object);
     entry = dictionary->FindEntry(entry);
@@ skipping 1127 matching lines @@
     }
   }
 
   DCHECK(j == result_len);
   return result_array;
 }
 
 ElementsAccessor** ElementsAccessor::elements_accessors_ = NULL;
 }  // namespace internal
 }  // namespace v8