Introduce a flag --limit-ints-to-64-bits in the VM in order to investigate the

runtime/lib/integers.cc

Index: runtime/lib/integers.cc
diff --git a/runtime/lib/integers.cc b/runtime/lib/integers.cc
index 36241789153360801feaaf5db8a11c36d2238eb9..a3fdc274f2b0f6eeb6a88bd0f180dc3f90ac81ea 100644
--- a/runtime/lib/integers.cc
+++ b/runtime/lib/integers.cc
@@ -409,6 +409,12 @@ DEFINE_NATIVE_ENTRY(Bigint_getDigits, 1) {
 
 
 DEFINE_NATIVE_ENTRY(Bigint_allocate, 4) {
+  if (FLAG_limit_ints_to_64_bits) {
+    // The allocated Bigint value is not necessarily out of range, but it may
+    // be used as an operand in an operation resulting in a Bigint.
+    Exceptions::ThrowRangeErrorMsg(
+        "Integer operand requires conversion to Bigint");
+  }
   // First arg is null type arguments, since class Bigint is not parameterized.
   const Bool& neg = Bool::CheckedHandle(arguments->NativeArgAt(1));
   const Smi& used = Smi::CheckedHandle(arguments->NativeArgAt(2));