[interpreter] source positions should not be emitted for dead code.

test/mjsunit/ignition/dead-code-source-position.js

Index: test/mjsunit/ignition/dead-code-source-position.js
diff --git a/test/mjsunit/compiler/regress-572409.js b/test/mjsunit/ignition/dead-code-source-position.js
similarity index 71%
copy from test/mjsunit/compiler/regress-572409.js
copy to test/mjsunit/ignition/dead-code-source-position.js
index 126b622625ad4455b4bd2e309ee10e32eb02989e..424c2e3a3fd30f03db15e6756d1cc3d4a6b00261 100644
--- a/test/mjsunit/compiler/regress-572409.js
+++ b/test/mjsunit/ignition/dead-code-source-position.js
@@ -2,9 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-var o = function() {};
+// Flags: --ignition-filter=f

[rmcilroy, 2016/02/04 15:06:39]

nit - no need for --ignition-filter=f

[Yang, 2016/02/05 12:21:31]

Done.

+
 function f() {
-  var lit = { __proto__: o  };
-  o instanceof RegExp;
+  for (f(x) in []) { f(new f()) }
 }
+
 f();