Backport hash collision workaround to 3.6.

src/heap.h

 // 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 61 matching lines @@
   V(Map, meta_map, MetaMap)                                                    \
   V(Map, hash_table_map, HashTableMap)                                         \
   V(Smi, stack_limit, StackLimit)                                              \
   V(FixedArray, number_string_cache, NumberStringCache)                        \
   V(Object, instanceof_cache_function, InstanceofCacheFunction)                \
   V(Object, instanceof_cache_map, InstanceofCacheMap)                          \
   V(Object, instanceof_cache_answer, InstanceofCacheAnswer)                    \
   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(FixedArray, empty_fixed_array, EmptyFixedArray)                            \
   V(ByteArray, empty_byte_array, EmptyByteArray)                               \
   V(FixedDoubleArray, empty_fixed_double_array, EmptyFixedDoubleArray)         \
   V(String, empty_string, EmptyString)                                         \
   V(DescriptorArray, empty_descriptor_array, EmptyDescriptorArray)             \
   V(Map, string_map, StringMap)                                                \
   V(Map, ascii_string_map, AsciiStringMap)                                     \
   V(Map, symbol_map, SymbolMap)                                                \
   V(Map, cons_string_map, ConsStringMap)                                       \
   V(Map, cons_ascii_string_map, ConsAsciiStringMap)                            \
@@ skipping 742 matching lines @@
   // the provided data as the relocation information.
   MUST_USE_RESULT MaybeObject* CopyCode(Code* code, Vector<byte> reloc_info);
 
   // Finds the symbol for string in the symbol table.
   // If not found, a new symbol is added to the table and returned.
   // Returns Failure::RetryAfterGC(requested_bytes, space) if allocation
   // failed.
   // 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));
   }
   MUST_USE_RESULT MaybeObject* LookupSymbol(String* str);
   MUST_USE_RESULT MaybeObject* LookupAsciiSymbol(Handle<SeqAsciiString> string,
                                                  int from,
                                                  int length);
 
   bool LookupSymbolIfExists(String* str, String** symbol);
   bool LookupTwoCharsSymbolIfExists(String* str, String** symbol);
@@ skipping 438 matching lines @@
   bool is_safe_to_read_maps() { return is_safe_to_read_maps_; }
 
   void CallGlobalGCPrologueCallback() {
     if (global_gc_prologue_callback_ != NULL) global_gc_prologue_callback_();
   }
 
   void CallGlobalGCEpilogueCallback() {
     if (global_gc_epilogue_callback_ != NULL) global_gc_epilogue_callback_();
   }
 
+  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();
 
   // This can be calculated directly from a pointer to the heap; however, it is
   // more expedient to get at the isolate directly from within Heap methods.
   Isolate* isolate_;
 
   int reserved_semispace_size_;
   int max_semispace_size_;
   int initial_semispace_size_;
@@ skipping 1035 matching lines @@
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG || LIVE_OBJECT_LIST
 
 
 } }  // namespace v8::internal
 
 #undef HEAP
 
 #endif  // V8_HEAP_H_