Implement ES6 completion semantics (--harmony-completion).

test/mjsunit/es6/block-for.js

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 171 matching lines @@
 assertEquals(undefined, eval("for (const i = 0; false;) { i; }"));
 assertEquals(undefined, eval("for (let i = 0; true;) { break; }"));
 assertEquals(undefined, eval("for (const i = 0; true;) { break; }"));
 assertEquals(undefined, eval("for (let i = 0; i < 10; i++) { continue; }"));
 assertEquals(undefined, eval("for (let i = 0; true;) { break; i; }"));
 assertEquals(undefined, eval("for (const i = 0; true;) { break; i; }"));
 assertEquals(undefined, eval("for (let i = 0; i < 10; i++) { continue; i; }"));
 assertEquals(0, eval("for (let i = 0; true;) { i; break; }"));
 assertEquals(0, eval("for (const i = 0; true;) { i; break; }"));
 assertEquals(9, eval("for (let i = 0; i < 10; i++) { i; continue; }"));
-assertEquals(3, eval("for (let i = 0; true; i++) { i; if (i >= 3) break; }"));
-assertEquals(2, eval("for (let i = 0; true; i++) { if (i >= 3) break; i; }"));
+assertEquals(3, eval("for (let i = 0; true; i++) { i; if (i >= 3) break; }")); // --harmony-completion: undefined
+assertEquals(2, eval("for (let i = 0; true; i++) { if (i >= 3) break; i; }")); // --harmony-completion: undefined
 assertEquals(
-  2, eval("for (let i = 0; i < 10; i++) { if (i >= 3) continue; i; }"));
+  2, eval("for (let i = 0; i < 10; i++) { if (i >= 3) continue; i; }")); // --harmony-completion: undefined
 assertEquals(undefined, eval("foo: for (let i = 0; true;) { break foo; }"));
 assertEquals(undefined, eval("foo: for (const i = 0; true;) { break foo; }"));
 assertEquals(3, eval("foo: for (let i = 3; true;) { i; break foo; }"));