Store RNG state on function context.

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 504261679e448b79aa4b15d0b47fc8d838a10b59..cbf33a75d4c353aa98875caccd9bf9ce53549afb 100644
--- a/src/runtime/runtime-maths.cc
+++ b/src/runtime/runtime-maths.cc
@@ -6,6 +6,7 @@
 
 #include "src/arguments.h"
 #include "src/assembler.h"
+#include "src/base/utils/random-number-generator.h"
 #include "src/codegen.h"
 #include "src/third_party/fdlibm/fdlibm.h"
 
@@ -244,5 +245,20 @@ RUNTIME_FUNCTION(Runtime_IsMinusZero) {
   HeapNumber* number = HeapNumber::cast(obj);
   return isolate->heap()->ToBoolean(IsMinusZero(number->value()));
 }
+
+
+RUNTIME_FUNCTION(Runtime_InitializeRNG) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 0);
+  static const int kSize = 4;
+  Handle<FixedArray> array = isolate->factory()->NewFixedArray(kSize);
+  uint16_t seeds[kSize];
+  do {
+    isolate->random_number_generator()->NextBytes(seeds,
+                                                  kSize * sizeof(*seeds));
+  } while (!(seeds[0] && seeds[1] && seeds[2] && seeds[3]));
+  for (int i = 0; i < kSize; i++) array->set(i, Smi::FromInt(seeds[i]));
+  return *isolate->factory()->NewJSArrayWithElements(array);
+}
 }  // namespace internal
 }  // namespace v8