Fix issue 5275: The VM must always generate the most compact form of an integer (Smi, Mint or Bigin…

runtime/vm/object.cc

Index: runtime/vm/object.cc
===================================================================
--- runtime/vm/object.cc	(revision 22813)
+++ runtime/vm/object.cc	(working copy)
@@ -10590,7 +10590,8 @@
         if ((cnt + right_value) >= Smi::kBits) {
           if ((cnt + right_value) >= Mint::kBits) {
             return BigintOperations::ShiftLeft(
-                Bigint::Handle(AsBigint()), right_value);
+                Bigint::Handle(BigintOperations::NewFromSmi(*this)),
+                               right_value);
           } else {
             int64_t left_64 = left_value;
             return Integer::New(left_64 << right_value);