Store RNG state on function context.

src/js/prologue.js

Index: src/js/prologue.js
diff --git a/src/js/prologue.js b/src/js/prologue.js
index 7aaad724c86fc2cc55a337eb2f36e610818a1050..b91a76562eed0d86e9bd6450e79cfcf77f66791e 100644
--- a/src/js/prologue.js
+++ b/src/js/prologue.js
@@ -245,6 +245,9 @@ function PostExperimentals(utils) {
     imports_from_experimental(exports_container);
   }
 
+  utils.InitializeRNG();
+  utils.InitializeRNG = UNDEFINED;
+
   utils.Export = UNDEFINED;
   utils.PostDebug = UNDEFINED;
   utils.PostExperimentals = UNDEFINED;
@@ -259,6 +262,9 @@ function PostDebug(utils) {
     imports(exports_container);
   }
 
+  utils.InitializeRNG();
+  utils.InitializeRNG = UNDEFINED;
+
   exports_container = UNDEFINED;
 
   utils.Export = UNDEFINED;