Constant propagation in LoadIndexed when inputs are array/string and index constants.

tests/language/guess_cid_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
-// Dart test program to test arithmetic operations.
+// Dart test program to test cid guessing optimizations.
 // VMOptions=--optimization-counter-threshold=10
 
 import "package:expect/expect.dart";
 
 main() {
   // Warmup optimizes methods.
   for (int i = 0; i < 100; i++) {
     Expect.equals(i, compareInt(i));
     Expect.equals(i.toDouble(), compareDouble(i.toDouble()));
     Expect.equals(i, binOpInt(i, i));
@@ skipping 64 matching lines @@
   for (int i = 0; i < N; ++i) {
     // Will trigger OSR. Operation in loop below will use guessed cids.
   }
   int sum = 0;
   for (int i = 0; i < N; ++i) {
     // Guess 'x' is Smi, but is actually Bigint: deoptimize.
     sum += x + 2;
   }
   return sum;
 }