Randomize the seed used for string hashing. This helps guard against

src/arm/code-stubs-arm.cc

 // Copyright 2011 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 5712 matching lines @@
   Register result = candidate;
   __ bind(&found_in_symbol_table);
   __ Move(r0, result);
 }
 
 
 void StringHelper::GenerateHashInit(MacroAssembler* masm,
                                     Register hash,
                                     Register character) {
   // hash = character + (character << 10);
-  __ add(hash, character, Operand(character, LSL, 10));
+  __ LoadRoot(hash, Heap::kStringHashSeedRootIndex);
+  // Untag smi seed and add the character.
+  __ add(hash, character, Operand(hash, LSR, kSmiTagSize));
+  // hash += hash << 10;
+  __ add(hash, hash, Operand(hash, LSL, 10));
   // hash ^= hash >> 6;
   __ eor(hash, hash, Operand(hash, LSR, 6));
 }
 
 
 void StringHelper::GenerateHashAddCharacter(MacroAssembler* masm,
                                             Register hash,
                                             Register character) {
   // hash += character;
   __ add(hash, hash, Operand(character));
@@ skipping 1566 matching lines @@
   __ StoreNumberToDoubleElements(r0, r3, r1, r5, r6, r7, r9, r10,
                                  &slow_elements);
   __ Ret();
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM