Make setting length on arrays faster.

src/objects.h

 // Copyright 2006-2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1143 matching lines @@
   inline bool HasDictionaryElements();
   inline bool HasPixelElements();
   inline bool HasExternalArrayElements();
   inline bool HasExternalByteElements();
   inline bool HasExternalUnsignedByteElements();
   inline bool HasExternalShortElements();
   inline bool HasExternalUnsignedShortElements();
   inline bool HasExternalIntElements();
   inline bool HasExternalUnsignedIntElements();
   inline bool HasExternalFloatElements();
+  inline bool AllowsSetElementsLength();
   inline NumberDictionary* element_dictionary();  // Gets slow elements.
 
   // Collects elements starting at index 0.
   // Undefined values are placed after non-undefined values.
   // Returns the number of non-undefined values.
   Object* PrepareElementsForSort(uint32_t limit);
   // As PrepareElementsForSort, but only on objects where elements is
   // a dictionary, and it will stay a dictionary.
   Object* PrepareSlowElementsForSort(uint32_t limit);
 
@@ skipping 3803 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_