Use a random seed for the string hash algorithm.

src/ia32/code-stubs-ia32.cc

Index: src/ia32/code-stubs-ia32.cc
===================================================================
--- src/ia32/code-stubs-ia32.cc	(revision 10321)
+++ src/ia32/code-stubs-ia32.cc	(working copy)
@@ -6033,10 +6033,20 @@
                                     Register hash,
                                     Register character,
                                     Register scratch) {
-  // hash = character + (character << 10);
-  __ mov(hash, character);
-  __ shl(hash, 10);
-  __ add(hash, character);
+  int32_t seed = masm->isolate()->HasherSeed();
+  if (seed != 0) {
+    ASSERT(FLAG_randomize_string_hashes);
+    // hash = (seed + character) + ((seed + character) << 10);
+    __ lea(scratch, Operand(character, seed));
+    __ shl(scratch, 10);
+    __ lea(hash, Operand(scratch, character, times_1, seed));
+  } else {
+    ASSERT(!FLAG_randomize_string_hashes);
+    // hash = character + (character << 10);
+    __ mov(hash, character);
+    __ shl(hash, 10);
+    __ add(hash, character);
+  }
   // hash ^= hash >> 6;
   __ mov(scratch, hash);
   __ shr(scratch, 6);