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

src/x64/code-stubs-x64.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 4940 matching lines @@
   if (!result.is(rax)) {
     __ movq(rax, result);
   }
 }
 
 
 void StringHelper::GenerateHashInit(MacroAssembler* masm,
                                     Register hash,
                                     Register character,
                                     Register scratch) {
-  // hash = character + (character << 10);
-  __ movl(hash, character);
-  __ shll(hash, Immediate(10));
-  __ addl(hash, character);
+  // hash = (seed + character) + ((seed + character) << 10);
+  __ LoadRoot(scratch, Heap::kStringHashSeedRootIndex);
+  __ SmiToInteger32(scratch, scratch);
+  __ addl(scratch, character);
+  __ movl(hash, scratch);
+  __ shll(scratch, Immediate(10));
+  __ addl(hash, scratch);
   // hash ^= hash >> 6;
   __ movl(scratch, hash);
   __ shrl(scratch, Immediate(6));
   __ xorl(hash, scratch);
 }
 
 
 void StringHelper::GenerateHashAddCharacter(MacroAssembler* masm,
                                             Register hash,
                                             Register character,
@@ skipping 1256 matching lines @@
                                  xmm0,
                                  &slow_elements);
   __ ret(0);
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64