While finding the valueOf descriptor, only look at the key entries.

src/arm/full-codegen-arm.cc

 // Copyright 2012 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 2717 matching lines @@
   // Calculate the end of the descriptor array.
   STATIC_ASSERT(kSmiTag == 0);
   STATIC_ASSERT(kSmiTagSize == 1);
   STATIC_ASSERT(kPointerSize == 4);
   __ add(r2, r4, Operand(FixedArray::kHeaderSize - kHeapObjectTag));
   __ add(r2, r2, Operand(r3, LSL, kPointerSizeLog2 - kSmiTagSize));
 
   // Calculate location of the first key name.
   __ add(r4,
          r4,
-         Operand(FixedArray::kHeaderSize - kHeapObjectTag +
-                 DescriptorArray::kFirstIndex * kPointerSize));
+         Operand(DescriptorArray::kFirstOffset - kHeapObjectTag));
   // Loop through all the keys in the descriptor array. If one of these is the
   // symbol valueOf the result is false.
   Label entry, loop;
   // The use of ip to store the valueOf symbol asumes that it is not otherwise
   // used in the loop below.
   __ mov(ip, Operand(FACTORY->value_of_symbol()));
   __ jmp(&entry);
   __ bind(&loop);
   __ ldr(r3, MemOperand(r4, 0));
   __ cmp(r3, ip);
   __ b(eq, if_false);
-  __ add(r4, r4, Operand(kPointerSize));
+  __ add(r4, r4, Operand(DescriptorArray::kDescriptorSize * kPointerSize));
   __ bind(&entry);
   __ cmp(r4, Operand(r2));
   __ b(ne, &loop);
 
   // If a valueOf property is not found on the object check that it's
   // prototype is the un-modified String prototype. If not result is false.
   __ ldr(r2, FieldMemOperand(r1, Map::kPrototypeOffset));
   __ JumpIfSmi(r2, if_false);
   __ ldr(r2, FieldMemOperand(r2, HeapObject::kMapOffset));
   __ ldr(r3, ContextOperand(cp, Context::GLOBAL_OBJECT_INDEX));
@@ skipping 1805 matching lines @@
   *context_length = 0;
   return previous_;
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM