[crankshaft] Make the for-in slow path compatible with the other compilers.

test/mjsunit/regress/regress-4715.js

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --allow-natives-syntax --dead-code-elimination --expose-gc
+
+var training = {};
+training.a = "nop";
+training.slow = "nop";
+delete training.slow;  // Dictionary-mode properties => slow-mode for-in.
+
+var keepalive = {};
+keepalive.a = "nop";  // Keep a map early in the transition chain alive.
+
+function GetReal() {
+  var r = {};
+  r.a = "nop";
+  r.b = "nop";
+  r.c = "dictionarize",
+  r.d = "gc";
+  r.e = "result";
+  return r;
+};
+
+function SideEffect(object, action) {
+  if (action === "dictionarize") {
+    delete object.a;
+  } else if (action === "gc") {
+    gc();
+  }
+}
+
+function foo(object) {
+  for (var key in object) {
+    SideEffect(object, object[key]);
+  }
+  return key;
+}
+
+// Collect type feedback for slow-mode for-in.
+foo(training);
+SideEffect({a: 0}, "dictionarize");
+SideEffect({}, "gc");
+
+// Compile for slow-mode objects...
+%OptimizeFunctionOnNextCall(foo);
+// ...and pass in a fast-mode object.
+assertEquals("e", foo(GetReal()));