Try flattening strings before comparing for equality.

src/heap.cc

 // Copyright 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 2062 matching lines @@
   } else if (length == 2) {
     // Optimization for 2-byte strings often used as keys in a decompression
     // dictionary.  Check whether we already have the string in the symbol
     // table to prevent creation of many unneccesary strings.
     unsigned c1 = buffer->Get(start);
     unsigned c2 = buffer->Get(start + 1);
     return MakeOrFindTwoCharacterString(c1, c2);
   }
 
   // Make an attempt to flatten the buffer to reduce access time.
-  buffer->TryFlatten();
+  buffer = buffer->TryFlattenGetString();
 
   Object* result = buffer->IsAsciiRepresentation()
       ? AllocateRawAsciiString(length, pretenure )
       : AllocateRawTwoByteString(length, pretenure);
   if (result->IsFailure()) return result;
   String* string_result = String::cast(result);
   // Copy the characters into the new object.
   if (buffer->IsAsciiRepresentation()) {
     ASSERT(string_result->IsAsciiRepresentation());
     char* dest = SeqAsciiString::cast(string_result)->GetChars();
@@ skipping 2407 matching lines @@
 void ExternalStringTable::TearDown() {
   new_space_strings_.Free();
   old_space_strings_.Free();
 }
 
 
 List<Object*> ExternalStringTable::new_space_strings_;
 List<Object*> ExternalStringTable::old_space_strings_;
 
 } }  // namespace v8::internal