Two minor bug fixes: a type error in the parser, and throwing the

dart/frog/leg/lib/js_helper.dart

 // Copyright (c) 2012, 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.
 
 #library('js_helper');
 
-$throw(String msg) {
-  var e = JS("Object", @"new Error($0)", msg);
-  var hasTrace = JS("bool", @"Error.captureStackTrace !== (void 0)");
-  if (hasTrace) {
-    JS("void", @"Error.captureStackTrace($0)", e);
-  }
-  throw e;
-}
-
 /**
   * Returns true if both arguments are numbers.
   * If only the first argument is a number, throws the given message as
   * exception.
   */
 bool checkNumbers(var a, var b, var message) {
   if (a is num) {
     if (b is num) {
       return true;
     } else {
@@ skipping 175 matching lines @@
   return UNINTERCEPTED(~a);
 }
 
 neg(var a) {
   if (JS("bool", @"typeof $0 === 'number'", a)) return JS("num", @"-$0", a);
   return UNINTERCEPTED(-a);
 }
 
 index(var a, var index) {
   if (a is String || isJSArray(a)) {
-    if (!(index is int)) $throw('Illegal argument');
-    if (index < 0 || index >= a.length) $throw('Out of bounds');
+    if (!(index is int)) {
+      throw new IllegalArgumentException(index);
+    }
+    if (index < 0 || index >= a.length) {
+      throw new IndexOutOfRangeException(index);
+    }
     return JS("Object", @"$0[$1]", a, index);
   }
   return UNINTERCEPTED(a[index]);
 }
 
 indexSet(var a, var index, var value) {
   if (isJSArray(a)) {
-    if (!(index is int)) $throw('Illegal argument');
-    if (index < 0 || index >= a.length) $throw('Out of bounds');
+    if (!(index is int)) {
+      throw new IllegalArgumentException(index);
+    }
+    if (index < 0 || index >= a.length) {
+      throw new IndexOutOfRangeException(index);
+    }
     return JS("Object", @"$0[$1] = $2", a, index, value);
   }
   return UNINTERCEPTED(a[index] = value);
 }
 
 builtin$add$1(var receiver, var value) {
   if (isJSArray(receiver)) {
     JS("Object", @"$0.push($1)", receiver, value);
     return;
   }
@@ skipping 162 matching lines @@
       return 1;
     } else {
       return -1;
     }
   } else if (a is String) {
     throw 'String.compareTo is not implemented';
   } else {
     return UNINTERCEPTED(a.compareTo(b));
   }
 }