Add a test for "is Object", fix try-catch of null

frog/corejs.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * Generates JS helpers for dart:core. This used to be in a file "core.js".
  * Having them in Dart code means we can easily control which are generated.
  */
 // TODO(jmesserly): one idea to make this cleaner: put these as private "native"
 // methods somewhere in a library that we import. This would be rather elegant
@@ skipping 225 matching lines @@
   var f = 'function(' + a.join(',') + '){return $f(' + p.join(',') + ');}';
   return new Function('$f', 'return ' + f + '').call(null, this);
 }""");
     }
 
     if (useStackTraceOf) {
       w.writeln(@"""
 function $stackTraceOf(e) {
   // TODO(jmesserly): we shouldn't be relying on the e.stack property.
   // Need to mangle it.
-  return e.stack ? e.stack : null;
+  return  (e && e.stack) ? e.stack : null;
 }""");
     }
 
     if (useToDartException) {
       w.writeln(@"""
 // Translate a JavaScript exception to a Dart exception
 // TODO(jmesserly): cross browser support. This is Chrome specific.
 function $toDartException(e) {
   var res = e;
   if (e instanceof TypeError) {
@@ skipping 17 matching lines @@
           // TODO(jmesserly): can this ever happen?
           res = new NoSuchMethodException('', e.arguments[0], []);
         }
         break;
     }
   } else if (e instanceof RangeError) {
     if (e.message.indexOf('call stack') >= 0) {
       res = new StackOverflowException();
     }
   }
-  // TODO(jmesserly): setting the stack property is not a long term solution.
-  // Also it causes the exception to print as if it were a TypeError or
-  // RangeError, instead of using the proper toString.
-  res.stack = e.stack;
+  if (res) {
+    // TODO(jmesserly): setting the stack property is not a long term solution.
+    // Also it causes the exception to print as if it were a JS TypeError or
+    // RangeError, instead of using the proper toString.
+    res.stack = e.stack;
+  }
   return res;
 }""");
     }
 
     if (useNotNullBool) {
       useThrow = true;
       // This pattern chosen because IE9 does really badly with typeof, and
       // it's still decent on other browsers.
       w.writeln(@"""
 function $notnull_bool(test) {
@@ skipping 133 matching lines @@
         w.writeln(@"function $wrap_call$1(fn) { return fn; }");
       }
     }
 
     // Write operator helpers
     for (var opImpl in orderValuesByKeys(_usedOperators)) {
       w.writeln(opImpl);
     }
   }
 }