Reland "Suppress canonicalization of Unbox() instruction that can deoptimize."

tests/language/vm/canonicalization_preserves_deopt_test.dart

+// Copyright (c) 2014, 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.
+// VMOptions=--optimization_counter_threshold=10 --no-use-osr
+
+import "package:expect/expect.dart";
+
+class X {
+  operator * (other) => "NaNNaNNaNNaNBatman";
+}
+
+foo(x) => (x * 1.0) is double;
+
+bar(x) {
+  try {
+    int i = (x * 1);
+    return true;
+  } catch (e) {
+    return false;
+  }
+}
+
+baz(x) => (x * 1) == x;
+
+main() {
+  for (var i = 0; i < 100; i++) {
+    Expect.isTrue(foo(1.0));
+    assert(() {
+      Expect.isTrue(bar(-1 << 63));
+      return true;
+    });
+    Expect.isTrue(baz(-1 << 63));
+  }
+  Expect.isFalse(foo(new X()));
+  assert(() {
+    Expect.isFalse(bar(new X()));
+    return true;
+  });
+  Expect.isFalse(baz(new X()));
+}
+