Bugfix: make dependent code field in AllocationSite weak.

test/mjsunit/regress/regress-320532.js

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+//
+// Flags: --allow-natives-syntax --smi-only-arrays --expose-gc
+// Flags: --track-allocation-sites --noalways-opt
+// Flags: --stress-runs=8 --send-idle-notification --gc-global
 
-// Flags: --allow-natives-syntax
 
-function foo(x) {
-  var a = [1, 2, 3, 4, 5, 6, 7, 8];
-  a[x + 5];
-  var result;
-  for (var i = 0; i < 3; i++) {
-    result = a[0 - x];
-  }
-  return result;
-}
-
+function bar() { return new Array(); }
+bar();
+bar();
+%OptimizeFunctionOnNextCall(bar);
+a = bar();
+function foo(len) { return new Array(len); }
 foo(0);
 foo(0);
-%OptimizeFunctionOnNextCall(foo);
-var r = foo(-2);
-assertEquals(3, r);
+%OptimizeFunctionOnNextCall(bar);
+foo(0);