Introduce runtime function %OptimizeFunctionOnNextCall to manually trigger optimization.

test/mjsunit/regress/regress-1210.js

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+// Flags: --allow-natives-syntax
+
 // Deoptimization of the key expression in an arguments access should see
 // the arguments object as the value of the receiver.
 
 var a = 0;
 
 function observe(x, y) { return x; }
 
 function side_effect(x) { a = x; }
 
 function test() {
   // We will trigger deoptimization of 'a + 0' which should bail out to
   // immediately after the call to 'side_effect' (i.e., still in the key
   // subexpression of the arguments access).
   return observe(a, arguments[side_effect(a), a + 0]);
 }
 
 // Run enough to optimize assuming global 'a' is a smi.
 for (var i = 0; i < 1000000; ++i) test(0);
+%OptimizeFunctionOnNextCall(test);
+test(0);
 
 a = "hello";
 test(0);