Allow Math.random to be called when creating a custom startup snapshot.

test/cctest/test-serialize.cc

Index: test/cctest/test-serialize.cc
diff --git a/test/cctest/test-serialize.cc b/test/cctest/test-serialize.cc
index 8477c384f3c245e3a8f844b4a9f8550d97149c60..c90ddb9c5d16ea0324cb1a6f44f160ab3da0a711 100644
--- a/test/cctest/test-serialize.cc
+++ b/test/cctest/test-serialize.cc
@@ -462,7 +462,8 @@ static void PartiallySerializeCustomContext(
           "  e = function(s) { return eval (s); }"
           "})();"
           "var o = this;"
-          "var r = Math.sin(0) + Math.cos(0);"
+          "var r = Math.random();"
+          "var c = Math.sin(0) + Math.cos(0);"
           "var f = (function(a, b) { return a + b; }).bind(1, 2, 3);"
           "var s = parseInt('12345');");
 
@@ -558,7 +559,18 @@ UNINITIALIZED_TEST(PartialSerializerCustomContext) {
                      ->ToNumber(v8_isolate->GetCurrentContext())
                      .ToLocalChecked()
                      ->Value();
-      CHECK_EQ(1, r);
+      CHECK(0.0 <= r && r < 1.0);
+      // Math.random still works.
+      double random = CompileRun("Math.random()")
+                          ->ToNumber(v8_isolate->GetCurrentContext())
+                          .ToLocalChecked()
+                          ->Value();
+      CHECK(0.0 <= random && random < 1.0);
+      double c = CompileRun("c")
+                     ->ToNumber(v8_isolate->GetCurrentContext())
+                     .ToLocalChecked()
+                     ->Value();
+      CHECK_EQ(1, c);
       int f = CompileRun("f()")
                   ->ToNumber(v8_isolate->GetCurrentContext())
                   .ToLocalChecked()