Support Smi->Double->HeapObject transitions in constructed Arrays.

test/mjsunit/array-construct-transition.js

+// Copyright 2011 the V8 project authors. All rights reserved.
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+
+// Flags: --allow-natives-syntax --smi-only-arrays
+
+support_smi_only_arrays = %HasFastSmiOnlyElements([1,2,3,4,5,6,7,8,9,10]);
+
+if (support_smi_only_arrays) {
+  a = new Array(0, 1, 2);

[Jakob Kummerow, 2011/12/07 17:02:47]

nit: "var a", please. Same for b and c.

[danno, 2011/12/08 15:09:09]

Done.

+  assertTrue(%HasFastSmiOnlyElements(a));
+  b = new Array(0.5, 1.2, 2.3);
+  assertTrue(%HasFastDoubleElements(b));
+  c = new Array(0.5, 1.2, new Object());
+  assertTrue(%HasFastElements(c));
+}