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

src/heap.h

Index: src/heap.h
===================================================================
--- src/heap.h	(revision 10328)
+++ src/heap.h	(working copy)
@@ -96,6 +96,7 @@
   V(FixedArray, single_character_string_cache, SingleCharacterStringCache)     \
   V(FixedArray, string_split_cache, StringSplitCache)                          \
   V(Object, termination_exception, TerminationException)                       \
+  V(Smi, string_hash_seed, StringHashSeed)                                     \
   V(Map, string_map, StringMap)                                                \
   V(Map, symbol_map, SymbolMap)                                                \
   V(Map, cons_string_map, ConsStringMap)                                       \
@@ -954,8 +955,7 @@
   // Please note this function does not perform a garbage collection.
   MUST_USE_RESULT MaybeObject* LookupSymbol(Vector<const char> str);
   MUST_USE_RESULT MaybeObject* LookupAsciiSymbol(Vector<const char> str);
-  MUST_USE_RESULT MaybeObject* LookupTwoByteSymbol(
-      Vector<const uc16> str);
+  MUST_USE_RESULT MaybeObject* LookupTwoByteSymbol(Vector<const uc16> str);
   MUST_USE_RESULT MaybeObject* LookupAsciiSymbol(const char* str) {
     return LookupSymbol(CStrVector(str));
   }
@@ -1506,6 +1506,12 @@
     return idle_notification_will_schedule_next_gc_;
   }
 
+  uint32_t StringHashSeed() {
+    uint32_t seed = static_cast<uint32_t>(string_hash_seed()->value());
+    ASSERT(FLAG_randomize_string_hashes || seed == 0);
+    return seed;
+  }
+
  private:
   Heap();