fixes #217, Object members on extension types

tool/sdk_expected_errors.txt

 warning: line 80, column 12 of dart:_interceptors/js_array.dart: [DownCastComposite] JS('var', r'#.pop()', this) (dynamic) will need runtime check to cast to type E
     return JS('var', r'#.pop()', this);
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 warning: line 125, column 9 of dart:_interceptors/js_array.dart: [DownCastComposite] JS('', '#[#]', this, i) (dynamic) will need runtime check to cast to type E
       f(JS('', '#[#]', this, i));
         ^^^^^^^^^^^^^^^^^^^^^^^
 warning: line 161, column 12 of dart:_interceptors/js_array.dart: [DownCastComposite] IterableMixinWorkaround.reduce(this, combine) (dynamic) will need runtime check to cast to type E
     return IterableMixinWorkaround.reduce(this, combine);
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 warning: line 169, column 12 of dart:_interceptors/js_array.dart: [DownCastComposite] IterableMixinWorkaround.firstWhere(this, test, orElse) (dynamic) will need runtime check to cast to type E
@@ skipping 16 matching lines @@
                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 warning: line 89, column 14 of dart:_interceptors/js_number.dart: [DownCastImplicit] JS('num', r'-Math.round(-#)', this) (num) will need runtime check to cast to type double
       return JS('num', r'-Math.round(-#)', this);
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 warning: line 91, column 14 of dart:_interceptors/js_number.dart: [DownCastImplicit] JS('num', r'Math.round(#)', this) (num) will need runtime check to cast to type double
       return JS('num', r'Math.round(#)', this);
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 severe: line 110, column 17 of dart:_interceptors/js_number.dart: [StaticTypeError] Type check failed: this (JSNumber) is not of type double
   toDouble() => this;
                 ^^^^
-severe: line 347, column 13 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.abs (() → num) is not a subtype of int.abs (() → int).
+severe: line 349, column 13 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.abs (() → num) is not a subtype of int.abs (() → int).
 class JSInt extends JSNumber implements int, double {
             ^^^^^^^^^^^^^^^^
-severe: line 347, column 13 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.unary- (() → num) is not a subtype of int.unary- (() → int).
+severe: line 349, column 13 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.unary- (() → num) is not a subtype of int.unary- (() → int).
 class JSInt extends JSNumber implements int, double {
             ^^^^^^^^^^^^^^^^
-severe: line 347, column 13 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.<< ((num) → num) is not a subtype of int.<< ((int) → int).
+severe: line 349, column 13 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.<< ((num) → num) is not a subtype of int.<< ((int) → int).
 class JSInt extends JSNumber implements int, double {
             ^^^^^^^^^^^^^^^^
-severe: line 347, column 13 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.>> ((num) → num) is not a subtype of int.>> ((int) → int).
+severe: line 349, column 13 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.>> ((num) → num) is not a subtype of int.>> ((int) → int).
 class JSInt extends JSNumber implements int, double {
             ^^^^^^^^^^^^^^^^
-severe: line 347, column 13 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.& ((num) → num) is not a subtype of int.& ((int) → int).
+severe: line 349, column 13 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.& ((num) → num) is not a subtype of int.& ((int) → int).
 class JSInt extends JSNumber implements int, double {
             ^^^^^^^^^^^^^^^^
-severe: line 347, column 13 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.| ((num) → num) is not a subtype of int.| ((int) → int).
+severe: line 349, column 13 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.| ((num) → num) is not a subtype of int.| ((int) → int).
 class JSInt extends JSNumber implements int, double {
             ^^^^^^^^^^^^^^^^
-severe: line 347, column 13 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.^ ((num) → num) is not a subtype of int.^ ((int) → int).
+severe: line 349, column 13 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.^ ((num) → num) is not a subtype of int.^ ((int) → int).
 class JSInt extends JSNumber implements int, double {
             ^^^^^^^^^^^^^^^^
-severe: line 347, column 13 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.sign (() → num) is not a subtype of int.sign (() → int).
+severe: line 349, column 13 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.sign (() → num) is not a subtype of int.sign (() → int).
 class JSInt extends JSNumber implements int, double {
             ^^^^^^^^^^^^^^^^
-warning: line 355, column 12 of dart:_interceptors/js_number.dart: [DownCastImplicit] this & ((1 << width) - 1) (num) will need runtime check to cast to type int
+warning: line 357, column 12 of dart:_interceptors/js_number.dart: [DownCastImplicit] this & ((1 << width) - 1) (num) will need runtime check to cast to type int
     return this & ((1 << width) - 1);
            ^^^^^^^^^^^^^^^^^^^^^^^^^
-warning: line 360, column 12 of dart:_interceptors/js_number.dart: [DownCastImplicit] (this & (signMask - 1)) - (this & signMask) (num) will need runtime check to cast to type int
+warning: line 362, column 12 of dart:_interceptors/js_number.dart: [DownCastImplicit] (this & (signMask - 1)) - (this & signMask) (num) will need runtime check to cast to type int
     return (this & (signMask - 1)) - (this & signMask);
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-severe: line 418, column 16 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.remainder ((num) → num) is not a subtype of double.remainder ((num) → double).
+severe: line 420, column 16 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.remainder ((num) → num) is not a subtype of double.remainder ((num) → double).
 class JSDouble extends JSNumber implements double {
                ^^^^^^^^^^^^^^^^
-severe: line 418, column 16 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.abs (() → num) is not a subtype of double.abs (() → double).
+severe: line 420, column 16 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.abs (() → num) is not a subtype of double.abs (() → double).
 class JSDouble extends JSNumber implements double {
                ^^^^^^^^^^^^^^^^
-severe: line 418, column 16 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.unary- (() → num) is not a subtype of double.unary- (() → double).
+severe: line 420, column 16 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.unary- (() → num) is not a subtype of double.unary- (() → double).
 class JSDouble extends JSNumber implements double {
                ^^^^^^^^^^^^^^^^
-severe: line 418, column 16 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.+ ((num) → num) is not a subtype of double.+ ((num) → double).
+severe: line 420, column 16 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.+ ((num) → num) is not a subtype of double.+ ((num) → double).
 class JSDouble extends JSNumber implements double {
                ^^^^^^^^^^^^^^^^
-severe: line 418, column 16 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.- ((num) → num) is not a subtype of double.- ((num) → double).
+severe: line 420, column 16 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.- ((num) → num) is not a subtype of double.- ((num) → double).
 class JSDouble extends JSNumber implements double {
                ^^^^^^^^^^^^^^^^
-severe: line 418, column 16 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.* ((num) → num) is not a subtype of double.* ((num) → double).
+severe: line 420, column 16 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.* ((num) → num) is not a subtype of double.* ((num) → double).
 class JSDouble extends JSNumber implements double {
                ^^^^^^^^^^^^^^^^
-severe: line 418, column 16 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.% ((num) → num) is not a subtype of double.% ((num) → double).
+severe: line 420, column 16 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.% ((num) → num) is not a subtype of double.% ((num) → double).
 class JSDouble extends JSNumber implements double {
                ^^^^^^^^^^^^^^^^
-severe: line 418, column 16 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.sign (() → num) is not a subtype of double.sign (() → double).
+severe: line 420, column 16 of dart:_interceptors/js_number.dart: [InvalidMethodOverride] Base class introduces an invalid override. The type of JSNumber.sign (() → num) is not a subtype of double.sign (() → double).
 class JSDouble extends JSNumber implements double {
                ^^^^^^^^^^^^^^^^
 warning: line 86, column 14 of dart:_interceptors/js_string.dart: [DownCastComposite] JS('JSExtendableArray', r'#.split(#)', this, pattern) (dynamic) will need runtime check to cast to type List<String>
       return JS('JSExtendableArray', r'#.split(#)', this, pattern);
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 warning: line 89, column 14 of dart:_interceptors/js_string.dart: [DownCastComposite] JS('JSExtendableArray', r'#.split(#)', this, re) (dynamic) will need runtime check to cast to type List<String>
       return JS('JSExtendableArray', r'#.split(#)', this, re);
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 severe: line 346, column 7 of dart:_interceptors/js_string.dart: [StaticTypeError] Type check failed: s += s (String) is not of type JSString
       s += s;
@@ skipping 969 matching lines @@
                       ^^^^^^^^^^^^^^^^
 warning: line 1869, column 12 of dart:core/uri.dart: [DownCastComposite] query.split("&").fold({}, (map, element) {int index = element.indexOf("="); if (index == -1) {if (element != "") {map[decodeQueryComponent(element, encoding: encoding)] = "";}} else if (index != 0) {var key = element.substring(0, index); var value = element.substring(index + 1); map[Uri.decodeQueryComponent(key, encoding: encoding)] = decodeQueryComponent(value, encoding: encoding);} return map;}) (dynamic) will need runtime check to cast to type Map<String, String>
     return query.split("&").fold({}, (map, element) {
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 warning: line 1901, column 12 of dart:core/uri.dart: [DownCastComposite] bytes.map((byteString) {int byte = int.parse(byteString); if (byte < 0 || byte > 255) {error('each part must be in the range of `0..255`');} return byte;}).toList() (List<dynamic>) will need runtime check to cast to type List<int>
     return bytes
            ^^^^^^
 warning: line 2023, column 12 of dart:core/uri.dart: [DownCastComposite] bytes (List<dynamic>) will need runtime check to cast to type List<int>
     return bytes;
            ^^^^^