[runtime] Speed up C++ version of ArrayPush

src/objects.h

 // Copyright 2015 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.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/allocation.h"
@@ skipping 2023 matching lines @@
   inline bool HasFixedFloat32Elements();
   inline bool HasFixedFloat64Elements();
 
   inline bool HasFastArgumentsElements();
   inline bool HasSlowArgumentsElements();
   inline bool HasFastStringWrapperElements();
   inline bool HasSlowStringWrapperElements();
   inline SeededNumberDictionary* element_dictionary();  // Gets slow elements.
 
   // Requires: HasFastElements().
-  static Handle<FixedArray> EnsureWritableFastElements(
-      Handle<JSObject> object);
+  static void EnsureWritableFastElements(Handle<JSObject> object);
 
   // Collects elements starting at index 0.
   // Undefined values are placed after non-undefined values.
   // Returns the number of non-undefined values.
   static Handle<Object> PrepareElementsForSort(Handle<JSObject> object,
                                                uint32_t limit);
   // As PrepareElementsForSort, but only on objects where elements is
   // a dictionary, and it will stay a dictionary.  Collates undefined and
   // unexisting elements below limit from position zero of the elements.
   static Handle<Object> PrepareSlowElementsForSort(Handle<JSObject> object,
@@ skipping 8778 matching lines @@
     }
     return value;
   }
 };
 
 
 }  // NOLINT, false-positive due to second-order macros.
 }  // NOLINT, false-positive due to second-order macros.
 
 #endif  // V8_OBJECTS_H_