Enable deterministic random number generation

src/runtime/runtime-maths.cc

Index: src/runtime/runtime-maths.cc
diff --git a/src/runtime/runtime-maths.cc b/src/runtime/runtime-maths.cc
index 4cb4f006ff380af45488f7ec9ae91d0d8c7ddc4c..75ed0f8e42ce5776cfbf0669c96f6246f4aa4ddc 100644
--- a/src/runtime/runtime-maths.cc
+++ b/src/runtime/runtime-maths.cc
@@ -38,6 +38,11 @@ RUNTIME_FUNCTION(Runtime_GenerateRandomNumbers) {
     state0 = double_to_uint64(cache->get_scalar(kState0Offset));
     state1 = double_to_uint64(cache->get_scalar(kState1Offset));
   } else {
+    // If a fixed random seed was requested, reset it whenever a script asks for
+    // random numbers for the first time in this context. This ensures the
+    // script sees a consistent sequence.
+    if (FLAG_random_seed != 0)
+      isolate->random_number_generator()->SetSeed(FLAG_random_seed);

[Yang, 2017/03/23 12:30:13]

I wonder whether it would be easier to simply set state0 and state1 to
FLAG_random_seed, and not touch random_number_generator at all, since its also
used elsewhere.

[Sami, 2017/03/23 17:00:27]

Sorry, missed this comment earlier. Yeah, that would be a simpler change. Done,
PTAL.

     cache = Handle<FixedDoubleArray>::cast(
         isolate->factory()->NewFixedDoubleArray(kCacheSize, TENURED));
     native_context->set_math_random_cache(*cache);