Fix inspect for the special case of an Object that inherits from Array, but has other properties.

lib/sys.js

@@ -92,7 +92,7 @@ var formatter = function(value, indent, parents) {
       if (parents.indexOf(value) >= 0) return '[Circular]';
       parents.push(value);
 
-      if (value instanceof Array) {
+      if (value instanceof Array && Object.keys(value).length === value.length) {
         return formatObject(value, indent, parents, '[]', function(x, f) {
           return f(value[x]);
         });

test/mjsunit/test-sys.js

@@ -13,6 +13,7 @@ assert.equal('null', inspect(null));
 assert.equal("\"\\n\\u0001\"", inspect("\n\u0001"));
 
 assert.equal('[]', inspect([]));
+assert.equal('[]', inspect(Object.create([])));
 assert.equal('[\n 1,\n 2\n]', inspect([1, 2]));
 assert.equal('[\n 1,\n [\n  2,\n  3\n ]\n]', inspect([1, [2, 3]]));
 
@@ -23,6 +24,9 @@ assert.equal('{\n "a": 1,\n "b": 2\n}', inspect({a: 1, b: 2}));
 assert.equal('{\n "a": {}\n}', inspect({'a': {}}));
 assert.equal('{\n "a": {\n  "b": 2\n }\n}', inspect({'a': {'b': 2}}));
 
-var value = {}
+var value = {};
 value['a'] = value;
 assert.equal('{\n "a": [Circular]\n}', inspect(value));
+value = Object.create([]);
+value.push(1);
+assert.equal('{\n "0": 1,\n "length": 1\n}', inspect(value));