Port a couple more stubs to x64.

runtime/lib/integers.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/bootstrap_natives.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/dart_entry.h"
 #include "vm/exceptions.h"
 #include "vm/native_entry.h"
@@ skipping 460 matching lines @@
                 Bigint::Handle(AsBigint(left)), right.Value());
           } else {
             int64_t left_64 = left.Value();
             return Integer::New(left_64 << right.Value());
           }
         }
       }
       result = left.Value() << right.Value();
       break;
     case Token::kSAR: {
+#if defined(TARGET_ARCH_X64)  // TODO(regis): Revisit.
+        int shift_amount = (right.Value() > 0x3F) ? 0x3F : right.Value();
+#else
         int shift_amount = (right.Value() > 0x1F) ? 0x1F : right.Value();
+#endif
         result = left.Value() >> shift_amount;
         break;
       }
     default:
       UNIMPLEMENTED();
   }
   ASSERT(Smi::IsValid(result));
   return Smi::New(result);
 }
 
@@ skipping 97 matching lines @@
 
 DEFINE_NATIVE_ENTRY(Bigint_bitNegate, 1) {
   const Bigint& value = Bigint::CheckedHandle(arguments->At(0));
   const Bigint& result = Bigint::Handle(BigintOperations::BitNot(value));
   ASSERT(CheckInteger(value));
   ASSERT(CheckInteger(result));
   arguments->SetReturn(Integer::Handle(AsInteger(result)));
 }
 
 }  // namespace dart