Properly set ElementsKind of empty FAST_DOUBLE_ELEMENTS arrays when transitioning.

test/mjsunit/regress/regress-117409.js

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+
+// Flags: --expose-gc
+
+function KeyedStoreIC(a) { a[0] = Math.E; }
+
+// literal with a fast double elements backing store

[Jakob Kummerow, 2012/05/09 15:02:58]

nit: Proper sentences with capitalization and full stop, please. (More below.)

+var literal = [1.2];
+
+// specialize the IC for fast double elements
+KeyedStoreIC(literal);
+KeyedStoreIC(literal);
+
+// truncate js array to 0 elements:
+//   backing store will be replaces with empty fixed array

[Jakob Kummerow, 2012/05/09 15:02:58]

nit: replaced

+literal.length = 0;
+
+// ArrayPush built-in will replace empty fixed array backing
+// store with 19 elements fixed array backing store.
+// Leading to a mismatch between the map and the backing store.
+// Debug mode will crash here in set_elements accessor.
+literal.push(Math.E, Math.E);
+
+// Corrupt the backing store!
+KeyedStoreIC(literal);
+
+// Release mode will crash here when trying to visit parts of E as pointers.
+gc();