Introduce a RandonNumberGenerator class. Refactor the random/private_random uses in Isolate/Context.

test/cctest/cctest.gyp

 # Copyright 2012 the V8 project authors. All rights reserved.
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@@ skipping 73 matching lines @@
         'test-lockers.cc',
         'test-log.cc',
         'test-mark-compact.cc',
         'test-mutex.cc',
         'test-object-observe.cc',
         'test-parsing.cc',
         'test-platform.cc',
         'test-platform-tls.cc',
         'test-profile-generator.cc',
         'test-random.cc',
+        'test-random-number-generator.cc',
         'test-regexp.cc',
         'test-reloc-info.cc',
         'test-semaphore.cc',
         'test-serialize.cc',
         'test-socket.cc',
         'test-spaces.cc',
         'test-strings.cc',
         'test-symbols.cc',
         'test-strtod.cc',
         'test-thread-termination.cc',
@@ skipping 112 matching lines @@
             '<@(_outputs)',
             'TEST',  # type
             'off',  # compression
             '<@(file_list)',
           ],
         }
       ],
     },
   ],
 }