Use stability to only conditionally flush information from the CheckMaps table.

test/mjsunit/regress/regress-map-invalidation-2.js

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 29 matching lines @@
     else return c;
   }
   // Clear type feedback from previous stress runs.
   %ClearFunctionTypeFeedback(f);
   return f;
 }
 
 var fun = g();
 fun(false, c);
 fun(false, c);
-fun(false, c);
 %OptimizeFunctionOnNextCall(fun);
 fun(false, c);
+%TryMigrateInstance(c);
+%OptimizeFunctionOnNextCall(fun);
+fun(false, c);
 fun(true, c);
 assertOptimized(fun);