Implement cryptographically secure random numbers by using crypto.getRandomValues.

sdk/lib/_internal/js_runtime/lib/preambles/jsshell.js

Index: sdk/lib/_internal/js_runtime/lib/preambles/jsshell.js
diff --git a/sdk/lib/_internal/js_runtime/lib/preambles/jsshell.js b/sdk/lib/_internal/js_runtime/lib/preambles/jsshell.js
index a33a58f1364579ccd9ac5b52d4fe4a3180489a88..9f136c28b962b9da8c91088ef0bd891fec35fcdf 100644
--- a/sdk/lib/_internal/js_runtime/lib/preambles/jsshell.js
+++ b/sdk/lib/_internal/js_runtime/lib/preambles/jsshell.js
@@ -67,6 +67,13 @@
       errorCallback(error);
     }
   };
+
+  // Mock cryptographically secure random by using plain random.
+  self.crypto = {getRandomValues: function(array) {
+    for (var i = 0; i < array.length; i++) {
+      array[i] = Math.random() * 256;
+    }
+  }};
 })(this)
 
 var getKeys = function(obj){