Harden %SetIsObserved with RUNTIME_ASSERTs

Now throws if its argument is already observed, or if the argument is
the global proxy.

BUG=371782
LOG=Y
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/274163002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21256 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/runtime.cc

@@ -14855,9 +14855,9 @@ RUNTIME_FUNCTION(Runtime_SetIsObserved) {
   HandleScope scope(isolate);
   ASSERT(args.length() == 1);
   CONVERT_ARG_HANDLE_CHECKED(JSReceiver, obj, 0);
-  ASSERT(!obj->IsJSGlobalProxy());
-  if (obj->IsJSProxy())
-    return isolate->heap()->undefined_value();
+  RUNTIME_ASSERT(!obj->IsJSGlobalProxy());
+  if (obj->IsJSProxy()) return isolate->heap()->undefined_value();
+  RUNTIME_ASSERT(!obj->map()->is_observed());
 
   ASSERT(obj->IsJSObject());
   JSObject::SetObserved(Handle<JSObject>::cast(obj));

test/mjsunit/es7/object-observe-runtime.js

+// Copyright 2014 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
+
+// These tests are meant to ensure that that the Object.observe runtime
+// functions are hardened.
+
+var obj = {};
+%SetIsObserved(obj);
+assertThrows(function() {
+  %SetIsObserved(obj);
+});
+
+assertThrows(function() {
+  %SetIsObserved(this);
+});