Speed up V8 random number generator, reverting part of 8490.

src/isolate.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 314 matching lines @@
 
 #endif
 
 #define ISOLATE_INIT_ARRAY_LIST(V)                                             \
   /* SerializerDeserializer state. */                                          \
   V(Object*, serialize_partial_snapshot_cache, kPartialSnapshotCacheCapacity)  \
   V(int, jsregexp_static_offsets_vector, kJSRegexpStaticOffsetsVectorSize)     \
   V(int, bad_char_shift_table, kUC16AlphabetSize)                              \
   V(int, good_suffix_shift_table, (kBMMaxShift + 1))                           \
   V(int, suffix_table, (kBMMaxShift + 1))                                      \
-  V(uint32_t, random_seed, 4)                                                  \
-  V(uint32_t, private_random_seed, 4)                                          \
+  V(uint32_t, random_seed, 2)                                                  \
+  V(uint32_t, private_random_seed, 2)                                          \
   ISOLATE_INIT_DEBUG_ARRAY_LIST(V)
 
 typedef List<HeapObject*, PreallocatedStorage> DebugObjectCache;
 
 #define ISOLATE_INIT_LIST(V)                                                   \
   /* AssertNoZoneAllocation state. */                                          \
   V(bool, zone_allow_allocation, true)                                         \
   /* SerializerDeserializer state. */                                          \
   V(int, serialize_partial_snapshot_cache_length, 0)                           \
   /* Assembler state. */                                                       \
@@ skipping 1007 matching lines @@
 
 } }  // namespace v8::internal
 
 // TODO(isolates): Get rid of these -inl.h includes and place them only where
 //                 they're needed.
 #include "allocation-inl.h"
 #include "zone-inl.h"
 #include "frames-inl.h"
 
 #endif  // V8_ISOLATE_H_