Dart2js: reflect of null gives error when invoking.

[lrhn]

Example:

import "dart:mirrors";
main() {
  var im = reflect(null);
  print(im.invoke(const Symbol("=="), [null]).reflectee);
}

gives:

reflectNull.dart.out:8820: TypeError: Cannot read property 'constructor' of null
    cache = t1.constructor[cacheName];

[peter-ahe-google]

Added Library-Mirrors, Accepted labels.

[peter-ahe-google]

Marked this as blocking #6490.

[kasperl]

Added this to the M7 milestone.

[kasperl]

Removed Priority-Unassigned label.
Added Priority-Medium label.

[kasperl]

Removed this from the M7 milestone.
Added this to the M8 milestone.

[floitschG]

https://codereview.chromium.org/161333002/

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Set owner to @floitschG.
Added Started label.

[floitschG]

Fixed in r32650.

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Added Fixed label.