Use a random seed for the string hash algorithm.

src/objects.h

Index: src/objects.h
===================================================================
--- src/objects.h	(revision 10321)
+++ src/objects.h	(working copy)
@@ -6117,7 +6117,7 @@
 
 class StringHasher {
  public:
-  explicit inline StringHasher(int length);
+  explicit inline StringHasher(int length, uint32_t seed);
 
   // Returns true if the hash of this string can be computed without
   // looking at the contents.
@@ -6168,7 +6168,9 @@
 
 // Calculates string hash.
 template <typename schar>
-inline uint32_t HashSequentialString(const schar* chars, int length);
+inline uint32_t HashSequentialString(const schar* chars,
+                                     int length,
+                                     uint32_t seed);
 
 
 // The characteristics of a string are stored in its map.  Retrieving these
@@ -6391,7 +6393,8 @@
   inline uint32_t Hash();
 
   static uint32_t ComputeHashField(unibrow::CharacterStream* buffer,
-                                   int length);
+                                   int length,
+                                   uint32_t seed);
 
   static bool ComputeArrayIndex(unibrow::CharacterStream* buffer,
                                 uint32_t* index,