[crankshaft] DCE must not eliminate (observable) math operations.

test/mjsunit/compiler/regress-4389-4.js

Index: test/mjsunit/compiler/regress-4389-4.js
diff --git a/test/mjsunit/compiler/regress-491578.js b/test/mjsunit/compiler/regress-4389-4.js
similarity index 55%
copy from test/mjsunit/compiler/regress-491578.js
copy to test/mjsunit/compiler/regress-4389-4.js
index c27570456c31e9a191fe1f4f1ea17b80f29de98e..e824973fac43efa3631b799f2fe3b93df8f93e29 100644
--- a/test/mjsunit/compiler/regress-491578.js
+++ b/test/mjsunit/compiler/regress-4389-4.js
@@ -2,14 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --allow-natives-syntax
+// Flags: --allow-natives-syntax --dead-code-elimination
 
-function foo(x) {
-  if (x === undefined) return;
-  while (true) {
-    while (1 || 2) { }
-    f();
-  }
-}
+function foo(x) { Math.round(x); }
+foo(1);
+foo(2);
 %OptimizeFunctionOnNextCall(foo);
-foo();
+assertThrows(function() { foo(Symbol()) }, TypeError);